The biggest differences in general between HTC and Samsung devices
1) launcher, do you like Sense or not, if no do you like Touch wiz (I have a verizon rezound, I find Sence the most appealing of all the UI overlays.
2) The camera, this I think is person to person, each company has their own strengths.
3) The screen technology: You have to look at an HTC screen next to a samsung screen and make that decision for yourself
4) How important is battery life for you. The HTC phones have come a decent way since the Thunderbolt but still do not have quite as much battery life as some of us would like to see.
The current flagship HTC phone (the HTC one) is not available on verizon and I have not heard any whisperings about when/if it is coming to verizon (I am not all that plugged into the rumor mill though). Currently the most up to date HTC phone is the Droid DNA, this phone was anounced last November (making it almost a dinosaur in smartphone years). I have been a pretty loyal HTC fan on verizon for the last 4 years or so but the lack of a current HTC phone is making me consider the galaxy S4. My upgrade does not come around till august though, so we will see what is in the pipeline then.
Hope this was helpful.
-spg