That Makita looks good, avoid the DeWalt like the plague. With cordless drills there are two key things to look for, battery type, Li-ion is what you want and the AmpHours Ah rating of the battery. The higher the Ah figure the longer the battery will last in use. The Makita is 3Ah which is pretty good, the DeWalt is 1.1 which is rubbish.
Watch it with branded tools, not all Makitas etc are worth having. I recently bought a Hitachi 18V with 2 3Ah batteries, cost a lot but was really worth the money, nearly got suckered into buying an on offer Makita from B & Q, glad I didn't, NI-Cad batteries and only 1.3Ah.
The voltage is only important if you're going to be using it for heavy duty drilling, if you have a corded drill it's not such an issue. An 18V will go through most things but a corded drill will be more powerful.
Weight can be a consideration, I bought the lads at work some nice Makita 14V ones but made sure the weight was low as they use them all day. So far they've been excellent (again 3Ah batteries).