Top fav is Garrus for not only being a total badass, but also for being a little bit naive and kind under that scaly exterior.
second comes Tali for being clever, cute, interesting and kickass all at once (I'm pursuing her in ME2). The quarians themselves are a very interesting species too. In fact Tali reminds me a lot of my girlfriend (there's way more than meets the eye to both of them, and they're both cute, smart and nerdy. XD)
And I like Wrex for wrexing everyone's !@#$ on a daily basis. I loved his little story about his asari friend he dueled. It was awesome.
Also, I'm starting to REALLY like the last guy you can recruit in ME2. You know, THAT one? He's pretty interesting.