Tonshathe majority of what you said is all preference
the S6 has a higher PPI than any other phone mentioned and is the only one with an OLED screen
iOS is a cleaner, and more effective UI for the vast majority of people (who care about UI). its also usually faster than most android phones.
the One is a lot easier to root (almost no barriers/deterrents from HTC)
the OP2 has less bloatware than any other phone besides the iPhone
not sure what part is personal preference besides maybe the iPhone UI thing