Clark has the more potential to be a better player. Baker probably won't get much better, though if he eliminates silly errors he could prove useful to us over the next 3 years. He's a back up for me. I wouldn't want him to be playing 30 games a season.
In terms of last season, Baker made errors but Clark was our worst center half. He was nightmarish at times. All over the shop. He needs to improve his upper body strength to make him better aerially, and his concentration a lot.
Those things are pretty key for a centre half, though.
So he just needs to improve his heading, not getting bullied off the ball, how he times his tackles and his marking (the latter two being linked to concentration, obv). If he doesn't already have that in his locker, it's a lot of ground to make up.
Not impossible, I suppose. But tough.
Personally, I think he's more likely to end up as a centre half lower down the leagues or as a defensive midfielder - for us, or for somebody else.
Baker is not without his deficiencies either, most notably his passing. But in the primary things you look for in a centre half, he is sound enough. The other things can be worked on, but the raw attributes are there.