Reshiram all the way. Dragon and electric is two of the types I don't like at all. The fire/dragon typing is rather nice though. For design I think both looks pretty cool to be honest. I haven't use any of them in battling yet so I can't say really.
Zekrom is awesome! He represents the dark part of Yin-Yang, has an awesome type combo and can turn into a ball of electricity.
Definitely Zekrom, which is why I bought White. In a way I wish I bought Black for battle city though but whatever =\
Zekrom is unique, as its types are dragon/electric. Idk, to me all dragons are assumed to be fire breathing. That's why I love Kyurem and Zekrom so much; they defy the common perception of dragons.