On the train (NY region) it appears that RIM’s Blackberry rule in the “smartphone” space of devices that enable a phone combined with email/web access.
If you need to access email primarily I would suggest you go with a Blackberry as the keyboard is MUCH easier to type on. However the NY Times appears to give the nod to the Treo 650 and writes
The Treo really shines, though, in the little touches that bear the pawprints of obsessive-compulsive designers. For example, it offers to add a newly dialed number to the address book, so you’ll have it for next time. You can look up a number in a thousand-name address book just by typing the person’s initials – and then dial with one key press. And the Treo’s physical Ringer Off switch is so brilliant and useful, it ought to become an F.C.C. requirement. Read the full article here