Well Im torn on this subject too. My current phone is painful to use and my upgrade is thursday. Now I have played witht he galaxy nexus and its an amazing phone, but I have had alot of issues with samsung in the past. My current breakdown of the phones:
HTC EVO 4g LTE
Pros: Everything! This is pretty much the perfect phone (for todays standards) and I have had a great track record with HTC on all my phones through them. Plus the support and accessories are amazing!
Con: Battery built in. This is a HUGE con and I mean HUGE! Sure the LTE radio is integrated into the CPU which is great for battery life. But phones of this caliber are notorious for bad battery life. Granted some days I can carry a small battery pack, but I cant every day and having my phone not last is not a good thing.
Galaxy nexus
Pros: Pretty much everything. The phone has been a blast to use at the store (and those floor models are notorious for lag and issues). I love the flow of ICS and never had an issue with touchwiz although Im a big sense fan.
Cons: Battery life, build quality, non expandable storage. The battery life has always been an issue with samsung phones, but the ability to get an extended battery or carry extra batteries is a plus. As always plastic materials. While the phone feels fine and seems durable, the plastic is a bit of a turn off. The lack of expandable storage isnt terrible but still a definite issue since Im down to 2GB of space on my current 16GB card which means Id fill the space of the galaxy immediately.
Conclusion:
If the new evo had a replaceable battery it would be a no brainer, but being limited to how long I can work away from a charger and/or having to lug around a battery pack is a big concern for me. Now if the new evo can get a full day on moderate to heavy use then its not a concern as by midnight I will have it on the charger. Hopefully the battery reports will come in soon so I can preorder or get the galaxy.