I wouldn't have another HTC after having a sensation XL, desire HD, and one M7, had issues with all three.
I fancied the S6 after my M7, but my HTC bit the dust about a week before it came out and I ended up with an iPhone 6 instead.
Not a massive fan of the way Apple railroad you into certain things though so I think a return to android is inevitable in the future, if you like to setup your phone to suit you the androids are much better.
The only thing the HTC has (had) over the samsungs was that the build quality was nicer with the metal frame, but the S6 has that as well now....