Jred had the best advice by far. Cnet is my 1st stop for research. They do a nice job describing the features enabling you to make a sensible decision.
As far as your question goes... it all comes down to what you're looking for. Blackberry's are great business tools. Their email integration is topnotch and feature a pretty simple user interface.
Downside?
For starters, it's keyboard is a cross between a qwerty and a traditional. Definitely takes some getting used to. Having had/used one before... I actually feel they are potentially better than qwertys for some... but definitely not all.
I'd say the most important factor (for me) is the fact that it's not a windows mobile device. for some, that's a good thing. for me, it's a deal breaker. windows mobile devices are basically portable computers. there's so much you can do... and it's rather easy to do them.
As far as the ipod goes... it's definitely a slick device but, for me, I could never get used to typing on a touch screen. I'm often calling (even typing) to people while driving... going by the feel of the phone. that's impossible with the iphone. In addition, no 3G... wickedly expensive... no stereo buetooth... inability to TRULY customize it... no replaceable battery... the list goes on. I'm hoping gen2 will address all/most of these issues.
For me... your absolute BEST option is the new AT&T Tilt. With all due respect to the incredibley overpriced/hyped N95, THIS is the best (smart)phone ever. (how can a smartphone not have a qwerty keyboard??? THAT is such a dealbreaker.... if it wasn't for that, the N95 would rock!) but yeah... the Tilt, though bulky, has EVERYTHING you could possibly want. With a service contract, the pricing is... reasonable. but expect it to go down with time. it's brand new.
good luck