I like both, but prefer the flat. Here is Silestone Lagoon with a flat (marble) subway tile.

1925 Plain & Fancy Kitchen - Dayton Ohio · More Info

The bevelled looks more interesting, richer.

I think the bevel makes it look more unique and high-end.

the bevels make me crazy. crazy. no idea why, makes no sense.

The only thing about the the beveled subway tile, is that at times can look a little bit heavy....and sometimes will look like Z-Brick to me.

I agree with the thistle's comment!