I would do expansion because it's the same game with balance tweaks and some new additions, pretty much.
Basically this, I first played the Vanilla version, and was too bored with the game to beat it a second time with the expansion. It adds lots of content, but early game is pretty much the same as vanilla. --- MSI 660 GeForce 2GB | i5 3570K Phantek PH-TC14PE_BK | AsRock Z77 Pro3 | 1500GBs HDD | Ballistix 8GB | Corsair CX430 http://www.anime-planet.com/users/StormKMD
My friends and I have preferred playing without the expansion once, and then with it always on. --- Another idea I had was the spy/sniper being able to climb into the soldier's rocket launcher and be launched across the map, dealing more damage, but no splash.
Playing without the expansion will make you appreciate it more when you do. For the most part, its the same game play just more levels and weapons --- You didn't try google, you made that up... Twist those dirty bags - Shake