3 most played:
Spah: 15 hours, 14 mins
Soldier: 3 hours, 12 mins
Medic: 2 hours, 30 mins
I can't stand playing as spy- but to each his own. I find the Medic can be fun, as can Engy.
I'm really looking forward to the Engy update. I'm pretty sure we'll see at least one or two of the following:
-Dispensi-trap: Replaces the regular dispenser with a cardboard box full of dynamite that LOOKS real to the enemy team; as soon as it's sapped or shot, it explodes!
-Bouncer: Replaces the teleporter with a similar device that launches the character using it with about as much force as the scout's double-jump, allowing such sneaky things as dropping a heavy in a top-floor window.
-Crita-spenser: Like a very pointy dispenser, allied units within it's radius get a boost to critical hit chances.
-Spearer: Replaces turret; unlike the regular turret, it has four ten-foot-long spikes. When an enemy gets within reach, it spears them for massive damage. Unlike a regular turret which is best placed at the end of a medium-long hallway, the spearer should be just behind the doorframe.
-Up-armor: A special wrench that is terrible for building, but can be used to "overheal" your equipment, giving you twice the time to save them.
-Hackwrench: Hitting a structure with this wrench will cause it to switch to your side, blowing up any old equipment of yours it might displace. Hitting an enemy with this does nothing, though if it made them see colors backwards for a random set of time, there could be fun. It can repair, but not upgrade things.
-Hoover: Replaces shotgun, or possibly pistol. A reverse gun that sucks up target items, turning them to metal or ammo, and just maybe picks up sticky mines. A successful taunt with this item picks up the enemies' hat, though the Soldier is so attached to his helmet that that might not be possible.
-Ammo Packer: Replaces builder remote. Takes metal and packs it up into tasty ammo units for allied characters. Allows Engies to help out the heavies, too! Potentially, a team of hoover-and-packer-packing Engies and medics could move ammo to a heavy like a bucket brigade.
I'd bet on the Crita-spenser more than anything else, though the ammo packer would be awesome.
What's really needed is a good way to get Engies involved in the combat instead of moping around the base. But you need to do that without making them actually be effective fighters. That's what I like about the Hackwrench and Crita-spenser, both of which are best used at the very front lines.
A simple Uber-sentry is unlikely, because as it is, they already are either killing you or not killing you. That binaryness is what makes them so balanced; a well-placed sentry is an immovable object, but a poorly-placed one is trash. What's essential to preserve is the way that it's all dependent on the engie's skill level.