Not really much that can be said because so far only Scoria is being released. any discussion is going to be based on prototype photos.

Fanstoys seems to have overwhelming support by everyone interested in MP Dinobots. Given their previous work on Quakewave, I can see why.

But, I'm holding out for Gigapower's set of Dinobots because they're taller.

If you want MP-03 Grimlock when he comes out, get him. He's a great figure.
But if you're the kind of collector that's concerned about scale (and lets face it, quite a few of us are), he is smaller than he should be. He's shorter than MP-10 Optimus Prime in robot mode. It seems most of the 3rd party Dinobots are making theirs bigger to scale properly with Masterpiece.