Roundman
Prince
Yeah, the Celts are very good, I agree. I don't think I've ever played the Germans. I'm put off by the UU. It must be one of the most useless.
I don't understand how you can say the Panzer is useless. The only downside to it is that it comes relatively late in the game. If your games get to that point (as my games tend to), they're very powerful (especially if you use them to trigger your GA and then go into mobilization). I have crushed many AI empires with Panzers, which are effective against everything up to Mechanized Infantry. I'd put them close to the top. Other than the Gallic Swordsman, the Mounted Warrior, the Chinese Rider, the Immortal, and maybe the Berzerker and Sipahi I'm hard pressed to think of a better UU.