I know what you mean with changing tastes... I think season 2 did a lot of that for me.

After season 1, my favourite was Rainbow Dash. The awesome, colourful one who can get things done! The others were all second favourite hehe.

After season 2, RD dropped down a bit (she was endearingly proud and confident in S1, but in some of the S2 episodes she crossed the line into obnoxiously arrogant), I took more of a liking to Fluttershy for reasons I can't fully put my finger on but I think mostly adjustments in my own personality during the influence of the fandom, and Pinkie shot up to be joint favourite with Flutters.

Why Pinkie? Smile episode and Baby Cakes. Suddenly she served more of a purpose than bouncing around not caring, character growth that she desperately needed and that really made me appreciate her so much more. Plus the stupid birthday episode that spawned "Pinkamena" (my least favourite part of the fandom with this obsession with turning a lovely bouncy character into a manically depressed psychopath) was long behind us by then :P