Which items to buy at All Random Deathmatch?

dota-2

In a All Random Deathmatch mode at Dota2 you get a new random hero each time you die, but keep all items you have bought before.
Which items is it worth to buy at All Random Deathmatch? Which items are bad to buy? How does your item choice should depend on here you have at the moment? What if you are support, should you still buy wards only and let the others lat hit?

ARDM is quite hard when it comes to picking items. However I have a build that has never (okay almost never) failed me so far. Here are some items that you can get on almost any hero and their benefit.

If you randomed a support

Well for now you get support duty which mean ward, courier and everything. You should not die that soon so for now aim for upgraded boots :

Tranquils are a great cheap choice but keep them only if you plan on roaming.
Power treads are the perfect fit and you can't (except in very rare situation like Tinker) go wrong with power treads.

What cheap "neutral" items to aim for ?

My favourite after the boots are :

As core

Orchid of Malevolence. Orchid gives attack speed, mana regen and a silence/burst. This item works on every hero. Because it gives attack speed even a right-clicker carry benefits from it. The mana regen is nice and the insta-silence does wonder. It's a great element of surprise aswell since few people expect an Orchid.
Blink Dagger or Force Staff. Any of those for escape is great however I prefer the Blink Dagger because it's initiation potential along with the orchid is great plus it also allows to disjoint projectiles.

As Situational

Vladimir's offering. Getting a Vlad later in the game is great. Vlad gives an armor aura, a mana regen aura and 15% damage. Plus if you are melee you'll get 16% lifesteal which is also nice. Note that the 15% damage only applies to base damages which means you don't get +15% damage from items like Demon Edge but only from item that boost your primary attribute (intel/str/agi). This is also why you get it later (when your stats are higher) and not early in the game
Mekansm. The sooner the better. Getting this item as mid arroud the 10 min mark allows your team to sustain through fights and start early pushes. It works on any hero.
Vanguard > Crimson Guard will boost your survivability and your team's one aswell and the bonus HP and HP regen is welcome on anyone.
Drums of endurance. Boost your survivability and your manapool. Give +9 to all attributes and the active is always nice to help chase or escape.

What luxury "neutral" items to aim for

Scythe of Vyse is good on anybody. It gives +10 to all stat (+ and extra 25 intelligence), plenty mana regen and a hard disable.
Heaven's Hallberd helps a lot to boost your survivability and gives and extra disable if someone is starting to right click too hard on the enemy team.
Black King Bar : if the game starts going longer a BKB is never a bad choice.
Sange and Yasha. Except on most intel heroes, Sange and Yasha will works for you since it gives all the stat required for a potential carry : Atack Speed, Move Speed, Agility, Strength and a passive slow. However if you are really rich you better go for...
... Eye of Skaadi. +25 All stats, Health, Mana and a slow debuff that goes through BKB.

My build almost always goes from Power Tread > Orchid > Blink Dagger > luxury of my choice. So far I have achieved 80+% winrate in ARDM.

I try to stick to very neutral items at first, and if I feel like I'm going to have a good game I'll start building more role specific items.

Boots

I will always get either Power Treads or Tranquils. Power treads are nice because they provide stats for every role. Tranquils are nice because they allow you to roam easier and keep you in lane longer. Both of these benefit almost every hero in the game a good deal. The other three boots are a lot more situational so I tend to avoid them, unless I'm rocking it as a hero who generally needs Boots of Travel.

Core

There are a handful of items I will get every game, and then some I'll get depending on my mood. For every game I like to get:

Aghanim's Scepter - This items has the stats, HP, and Mana that every hero can benefit greatly from. There are a ton of ultimates in the game that are improved by this item, and it seems every major patch Icefrog is adding more ultimates to that list. You really cannot go wrong with grabbing this. It's generally the item I build right after my boots, even if I don't currently have a hero that has an ultimate that applies.
Blink Dagger - Every game. Every hero can benefit from. I don't care if your hero already has amazing escape, get this. It gives you just one more, which will keep you alive longer and gives you the ability to get the jump on the enemy team.
Black King Bar - This item will make sure you can go into fights and not be disabled the entire time. BKB ensures that you actually remain useful during engagements, and greatly aids in your survivability. Plus it gives you a little bit of strength (health) and damage.
Orchid Malevolence - This is generally my last item. It gives a lot of intelligence, attack speed, damage, and mana regen. Attack speed and damage benefits everybody, intelligence and mana regen benefit most everybody to a lesser extent. The active is what we want here though: A 5 second silence + damage amplification! That 5 second silence is an eternity in Dota. With it you can just entirely shut down their support or any big ult they have. A well timed and placed Orchid can win fights.

Situational

These are items I get really depending on my mood. It's hard to have situational builds in ARDM since the situation is constantly changing.

Sange and Yasha - I get this probably half the time. It has pretty nice stats, good movement speed increase, and the maim is useful for ensuring heroes don't get away from your team.
Mekansm - I just realized how weird this item is spelt. Anyways, this item benefits your whole team! If I'm feeling supporty and nobody else is building one, I'll grab this pretty early on. This once lead to humorous game where I randomed Riki first, expected to die soon so I start going a support build. Ended up never dying, had Tranquil boots, Mekansm, Aghanim's, and BKB. Was a weird build, but hey it worked.
Pipe of Insight - This is a pretty good item. Lets your team block a good bit of magic damage (400 I think). If they keep getting big spell casters then pick this up to keep your team alive through the nukes.
Urn of Shadows - This item is incredibly cheap and incredibly useful. If I'm feeling supporty and someone else grabbed Mekansm, then I'll grab this. Or I'll grab both! Having a Mekansm and Urn of Shadows on your team means nobody ever has to go back to the fountain. You are a mobile fountain! The DoT also helps make sure nobody gets away with 17 HP.
Force Staff - Another incredible utility item. Need an escape? Force staff! Need to chase down someone? Force staff! Want to surprise that annoying Drow hiding behind their tower shooting you? Force staff her into your face! Such a great and fun item it's hard to ever pass this up. This item is so good it might need to be a core item.
Shadow Blade - This is an item I like to get very occasionally. There are a good number of heroes that this item is basically on a must on, and every hero barring Riki and Clinkz benefit a little bit from this. It helps initiate fights, helps you escape, helps you gank, and you even get a good bit of damage from it. And if you happen to random a Witch Doctor in the game and you have your Shadow Blade, oh man. Not much is scarier than an invisible Witch Doctor Aghanim ultting your team.

Of course depending on how "situational" we want to get, this list could go on for a very long time. But these are probably my top situational items I get in ARDM.

Misc.

These are items I didn't mention above because they're just so cheap, but you should be aware of them.

Magic Wand - This items is so awesome. Every single hero in the game benefits from this. It is super cheap (500 gold I think), and provides free heals and mana all game!
Observer Wards - Someone has to buy these. In ARDM, everyone should be playing a little bit of support. This means occasionally you'll need to buy wards. Don't ever let the shop have 2 stacks, and if you look and there are 2 stacks sitting there, buy a set! I don't care if you're a 7 slotted Void, buy the wards.
Sentry Wards - You should be dewarding, but I know in pubs that doesn't happen very much. If you're feeling good and you're pretty sure they're warding you, then buy these. Or if they just have a stealth hero obviously grab these.
Gem - This is item relatively cheap at 900 gold, but lets you deward everywhere you go. Also puts an end to any stealthing the enemy team wants to do (and if they read my guide, then they will all have Shadow Blades!).

These are just the items I tend to look at in ARDM. The other suggestions are also great and could supplement this list. Utility items are always a good pick in ARDM as they benefit everybody. The only real utility item I do not recommend is Linkens Sphere, as WizLiz has covered in their post. Even the utility is amazing, it is just too situational.