One of the standards that was taught in bygone days (when people actually made an effort to learn and uphold some standards of English) was to use the preposition "with" with the word "compare".
"Compared with" used to mean something different from "compared to".
"Compared with" was used to mean what most people, these days, have transposed to "compared to". "Compared to" was used to mean "liken to", as in the Shakespearean line, "Shall I compare thee to a summer's day?"
I know that, these days, the vast majority of native English speakers don't bother to maintain this standard, but there are still some who haven't gone to the grave.
"In comparison with you, I am more friendly" should certainly be accepted.
Yes, both are OK. "She seems more friendly than him" or "She seems friendlier than him" are both fine in spoken English.