No, what you think is "being nice" is actually "refraining myself from telling what I truly think".
Taylor Swift is the nicest, although many people don't get that because she was born with a angry face.
No way.
I'd say it's definitely either gaga or taylor.
Aside from recent times gaga never ever shaded other people and is always sweet and lovely in public and in interviews.
Taylor also seems incredibly lovely and genuine. (People might say she's a bit of a bitch due to her occasional shade at her exe's when accepting awards and stuff but I think most of that is pure publicity anyway and isn't genuine).