Can't comment on the HTC, but I love my S4.
Coming from a long history of iPhones it was a revelation and I wouldn't change it.
Lots of gimmicks that I don't use like, but plenty that I do. The screen is nice and big, and very very clear.
Stock keyboard and spellcheck is crap, but you can download a variety of types for free from the Play store.
I'd say it's essential to get a case for it from the start, as I scratched my camera a little bit on a table as the lense is flush with the back.