All three of those look like they'd be fun to play with. For obvious reasons, Gray would go well with Weiss. Do you have any preference concerning which of the three characters I mentioned you would like to play with?
Hmm... I choose Neo. It would be an interesting dynamic: Gray confessing to Neo, and Neo being ordered by Cinder to try and use him, since he's an heir. And since Neo is mute(?) perhaps Gray knows sign since, say, his mother is deaf.
I have honestly never used Gray in a RP, so I'd like to use him. A funny idea would be him in a sorta-harem situation with all three (childhood friend, the girl he likes, and the jealous Neo who wants Gray to stay away from Cinder-senpai but won't admit to herself she kinda likes him). XD
That idea of Gray having a crush on Cinder was one I had bouncing around in my head, since nobody did an honest to God confession of love in the first three volumes. But I'd be happy with any of them.