Seekins, Nightforce, Badger, Sphur, JP, MPA, all solid options.
The only downside I've seen to the Seekins is if you rail is undersized at all, the rail clamps can bottom out and the mount won't hold. Happened on my last Mega large frame upper build, run them on 2 other Mega uppers without issue, but even on those the clamp is so close to bottoming you almost can't see the gap.