When is the Kritzkrieg preferable to the Medigun?

Solution 1:

First, you need to look at when the übercharge is useful: taking out entrenched engineer nests, and leading a strong push. This makes übercharge particularly useful for spearheading an assault.

On the other hand, the Kritzkrieg is useful for countering a push, because it lets someone push out a large amount of damage in a short span of time. Use the kritzkrieg to clear contested points, hunt down regrouping enemies, etc.

The Kritzkrieg also charges faster. If you're finding you often die before you get a chance to deploy an übercharge, you might try switching to the kritzkrieg, as you'll build up the kritz-über faster.

Solution 2:

While the answer is situational. Lets cover the basics first:

Healgun name | Übercharge Effect | Charge time
----------------------------------------------------------------
Medigun      | Invincibility     | Baseline
Kritzkrieg   | Critical hits     | 25% faster than Medigun
Quick Fix*   | Fast Heal         | 50% faster than Medigun

*New in TF2 Beta, also speeds you up when healing a faster target, such as a Scout. However, it has no overheal, although you can continue healing targets to build your Übercharge.

Now for some scenarios:

• The Medigun is the most useful if you have the time to charge it. If there is a map setup time and you choose medic near the start of it, you should always use the Medigun.
• The Medigun has the biggest benefit from equipping the Vita-Saw because it takes the longest to charge.
• Critical Hits do not do bonus damage to buildings. You need the Medigun or Quick Fix to break Sentry Farms. It is recommended you use the Medigun to take out Sentry farms.
• The Kritzkrieg is really useful at the start on 5cp maps, because it charges faster. It can be a great boon to taking the middle point due to its increased charge speed.
• The Quick Fix (the new healing gun in Beta) can be useful if you want to reach the front line quicker. If you heal a Scout, you speed up to Scout speed. Its increased charge time means you'll also be able to use it more often than the other two.
• The Übersaw adds 25% to your Übercharge meter regardless of which medigun you have.
• Any of the three can be useful when defending a point. Keep in mind that Quick Fix and Kritzkrieg both charge faster, and thus can be used more often.

So, the rule of thumb is to start with the Medigun if there are setup gates. Be aware that the walls can be jumped on cp_well. Use the Medigun to take down Sentry Guns. Kritzkrieg works well for pushes against sets of enemies that have no sentry farms. Quick Fix is still new and may be useful in one of these two situations, I haven't tested it enough to tell.

Solution 3:

The Kritzkreig leaves your target open to damage, making it less useful in games with many players (and a lot of damage going out). It works best on soldiers and demos, because they can do damage without getting close to the fight. Also, critical rockets and grenades quickly take out players surrounding a sentry, so the Kritzkreig uber will kill Engineers repairing sentries. The Medigun's uber will have a harder time killing engineers because there is no bonus damage against players.

Also, the Kritzkreig charges quicker than the Medigun. If you're losing or trying to take a capture point the Kritzkreig will both charge faster and provide more damage output to clear the point, especially on Soldiers and Demomen (once again).

In short: use the Kritzkreig for destroying big Engineer setups that you can fire at from a distance, or to clear capture points. Otherwise you will have better luck with the Medigun when you have enough time to charge it.

Solution 4:

You already got some good answers, so I only add a point that could be useful and hasn't been mentioned yet.

Due to the fact that most servers have 24 slot or even 32 slots in order to have some chances to win your team usually needs at least two medics, sometimes three.

In this case having one medic with medigun and one with kritzkrieg guarantees good team flexibility. An übercharge used to destroy the sentryguns or the opponent heavy+medic duo followed by a kritzcharge could be extremely painful and could break stalemate situations.