How many are pre-ordering this or is it a wait, listen and see type of stance?
AT&T generally has better signal strength than Sprint, so I wouldn't get too excited about battery life comparisons just yet.
Hopefully, this phone's battery will be able to go on through out the day even with low signal (the coverage here can be kind of bad).
I get craptastic signal (with AT&T) at work, and I can usually make it through the day without having to charge my 4S. But I have a tendency to hammer it pretty hard by surfing the web and listening to music, so I don't know if I'd call my usage pattern typical. That said, the EVO (if I'm not mistaken) has a larger battery than the iPhone 4S, so depending on how you use the phone you might not have an issue.