I like Davin Felth. According to the EU, he was in the stormtrooper armor corps until he started publicizing weaknesses in the AT-AT and got reassigned to the infantry. I kind of sympathize with his conundrum. You don't want to tell a superior officer that his multi-million dollar system is rendered useless by poor doctrine which said officer probably spent years studying or preaching, but if you don't you're putting your unit and your mission at risk. He's also the "look sir, droids," guy.
TK-421 is also pretty cool.