Countering Marines, Marauders and Tanks

Solution 1:

For protoss you have to make excellent use of Sentries to delay your enemy. If possible, try to split his army in two with Force Field(s) and take on that half by itself with your zealots, sentries, and stalkers. You won't be able to take him in a head-on fight as Marines/Marauders dominate your T1 units.

Use this delaying tactic to get a few Immortals as soon as possible and transition into Colossus with the range upgrade. The splash damage is very effective against the tightly clumped Bio Ball, while Immortals can take many hits from Siege Tanks. Use Blink Stalkers to get close to the tanks and focus them down. Note that once you have a few Colossi, your opponent will usually get a few vikings to counter them, but focus them down quickly with your stalkers.

Honestly, it is a very difficult thing to beat as Protoss if your opponent is of better or equal skill, especially since you have to tech to very expensive units just to counter his (mostly) T1 army. You'll just have to delay and outplay them and not make any mistakes, and make sure you are very proficient with your Force Field and Guardian Shield usage.

Another option is to go High Templars with Psionic Storm and Feedback on the Medivacs, but I rarely go this route as it is too gas-intensive and higher level Terran players will just use Ghosts which nullify High Templars with their EMP ability (Removes all energy and 100 shield points). Not to mention if your clump of High Templars goes within range of a Siege Tank you're dead meat.

Solution 2:

At lower leauge levels such as bronze, it's not so much about having the right counter units; people generally know what counters what.

What's most important is knowing your fundamentals and doing it fast (building probes, not getting supply blocked, and macroing).

Having said that, I would recommend finding a good solid and stable build order. Memorize it, practice it, and be able to execute it flawlessly.

If you are still concerned about MMT, a standard 3 gateway and Robo build will do just fine in most cases as Immortals are a good counter to both Tanks and Marauders. Following up with Colossi works well too.

Taken from Liquipedia, this build is intended for Zerg, but with minor tweaks (maybe get a stalker earlier) it will adapt just fine for most Terran builds and strategies at bronze levels.

9 Pylon

10 Chrono Boost Nexus after Pylon finishes

12 Gateway #1, send scouting Probe

13 Chrono Boost Nexus

14 Assimilator #1, 3 on gas when finishes

15 Pylon

16 Zealot

18 Cybernetics Core

21 Zealot

23 Sentry

24 Warpgate research

24 Zealot

25 Pylon

25 Assimilator #2

27 Robotics Facility

28 Gateway #2

32 Observer

33 Pylon

35 Immortal

39 Gateway #3

Solution 3:

Coming as a zerg player, MMT is usually in a big fat ball so splash damage really is the best choice. Banelings can practically one shot a ball like that, if burrowed and timed correctly.

On the toss side my first guess would be a good mix of zealots and stalkers (with blink).

Solution 4:

Many of these answers are highly focused on unit choice, which is meh. StarCraft is not about getting the magical mix of units that will pwn the other guy's units. The standard armies of each race will do fine. The important thing is of course macro. To beat his army you should simply have more stuff.

That being said, basic micro is important as well. You need to have your units attack together, not in a limbo line, you need to have good surface area, make a decent arc, and engage in favorable terrain, make sure your zealots are not stuck behind your stalkers.

I'm dubious of bronze level player's abilities to use sentry and phoenix well, and so I would advise leaving them out. vs MM tank good positioning is vastly more important.

Colossus and High Templar both counter bio though, but remember that they're support units. It's still much more important to have good positioning with your army.

Solution 5:

A good counter unit composition would be zealots and immortals. Immortals are a hard counter to mauraders and tanks. Zealots to defend the immortals from marines.

A psi storm or two will work wonders on a big bio-ball.