A friend has a Snap On 18v and a Bosch. Both work faultlessly, but the Bosch does have more power.

I'd stick with a big name though if buying one. I always hear of people with Sealey or other similar brands saying they cant undo wheel nuts etc, although Ive never used one myself.

Bosch, Makita, Hitachi, Panasonic etc but they are going to cost a few quid.