If cost is not a factor and you don't care about having a U.S. warranty, the E61. It is obviously more capable, and an unlocked phone really works out better for the international traveller.
On the other hand, you can get the E62 for free or almost free if you are a new Cingular customer. Check Cingular's website or Amazon for pricing.
I guess the basic question is probably, is it worth paying extra for WiFi, an unlocked phone, or extra overseas roaming capabilities.
The answer for me is "yes", but then I'm not a Cingular customer anymore and have no intention of going back to Cingular, so an E62 isn't an option.