Ok, I won't make this a long post! As some others have stated, I use both devices. There both great. And this is what I'll say: no matter what, a bb will always be on my waist in an oem leather case....it's the best device on the planet for, emailing, texting, bbm is great, and for phone calls. On the flip side, my 3Gs is just as good for making calls, that is when there not getting dropped in NYC..lol, and is awesome for Internet use, music (iPod after all) aps, gaming, and general use. Granted, there both the best at what they do! And I'll most likey continue to use both until RIM really puts a serious web kit on future devices, but by then a new iPhone will have arrived, and who knows how crazy that will be!
All in all, get both if ya can...lol! Seriously, as everyone pretty much said, it just really all depends on what u need it for. Both are great, so good luck.