I've played MNK since ARR.
Pain.

I am looking forward to MNK the most.
I actually like what I saw of SAM too tho, it already plays really nicely so I like that they just added something extra on top of it and the new big hitter looks awesome.
RDM actually looks really cool too I love the visuals of the line attack spell.
And GNB has only improved upon imo, another big two cart hitter and continuation on burst strike.
Really nice.

I'd say all of them looks amazing lol I feel like I want to play everything.
But I think that MNK, GNB and SAM is what I will stick with but I want to test Sage too and probably Reaper.
Issue I have is that Reaper will be so extremely popular and all over the place it was the same with SAM I only really started playing it after it had calmed down I don't like playing the same as everyone else.