Depends... Do you want a touchscreen or a regular keypad. Me personally I like the keypad so I say Bold. The Bold is a great device and I am sure the Storm is as well. You just got to figure out your preferences.
Really depends on what you want and need in a phone.
Try looking at the specs for each and use that as a starting
point. There are also a ton of discussions of both phones on this
site in the sections dedicated to each.