Posting or sitting???

I just started taking lessons 4 months ago. I want to ride Western pleasure. My first trainer taught to sit the trot and canter. Slide your butt on the saddle in rythym. We I have a new trainer now and she says you have to post. (She has a english mentality). So now Im trying to learn to post in a western saddle. (John Wayne would NOT be proud of me). I like sitting better. So is posting or sitting better??

I used to post in western saddle as long as the gait was any faster than a jog. So if you do a real trot I think it's easier on horse's back when you post.

Yes, it's easier on the horse's back, and usually easier on YOUR back when you've become experienced at posting.