Who do you uber first?

Demomen for me. They always get the job done

i save my uber til its needed lol mostly a pyro tho they go in and cause destruction, i sometimes ubermyself if im in trouble or i just taunt at people and make them mad

You're both wrong.

You uber BattleSniper first.

TF2F_mtnsean and ubiquitous, smokey, and rambo. but pyroes are always fun to uber since everyone burns in hell.

Now, granted who to uber is really situational. 

I think the most important thing to remember is what you need to to after you hit the uber.  If you are hunting turrets get your skinny medic behind out in front of your target so that you can take the fire from the sentry instead of your damage dealer.  (This is especially important if you are ubering a Pyro or Heavy who are most effective at close range.)   If they can get the right range I think Pyros are the best sentry sweepers.

My two favourite classes to uber are Heavys and Pyros.  I almost never uber a soldier.

Quote:

Only if Battlesniper is playing spy.

I do agree with 22mojom22 - who you uber is defintely situational.  I liked the tip that you should get your ubered medic butt out there so the close-ranged damage dealers can take down the sentry guns.

Typically, I like to uber pyros, demos, and heavies.  Pyros are, of course, great for large bunches of baddies in close range.  Demos are great for the sentry guns and nasty snipers or other solos that are causing you troubles.  And heavies - well, they're just fun to uber.  Good for all of the above.

~ Dia

if it is not a situation that calls for a certain class (such as needing a demo to clear an sg nest) then I will try for heavy or pyro first.

Unless cypher is on my team.  There is nothing like watching cypher go aggro-uber-engy and get in a bunch of wrench kills.  Pure enjoyment.  Plus I get to spread the love to a fellow engy.

If the sentry is close around a corner, a heavy. If it is out of range of a heavy, a demo. The reason for this is because a heavy can generally do more damage after the sentry is down, the demo has used up part of his clip to take the sentry down. If all I want to do is kill people usually a heavy or soldier, even if they are bad they can still get some kills. If I know a good demo is on my team I'll uber him sometimes.

If it's to take out a sentry: a demo.

If it's to take out a number of soft targets: a soldier.

If it's to take out a number of soft targets in a small area: heavy.

If it's to block of an area for something (for example, to camp the enemy spawn while we cap a point) heavy.

If it's to drive a number of people AWAY, pyro.