Plain old Wal-Mart orange foam plugs, covered by a pair of Peltor low-profile (Tactical 6?) earmuffs with behind-the-neck band.
Just one or the other is not enough, especially if doing any sort of moving around. For example, when shooting a Highpower Match, it's easy to knock earmuffs off center when getting into the sitting or prone position from standing. If you're not wearing plugs underneath, you are immediately exposed to the full fury of the guy shooting the M1A next to you! And of course, you are too focused on the match stage to stop and fix the situation, so you just grin and bear it.
Nope - always go with double protection. This is especially true if you have some hearing loss like I do from a few stupid days on the range in the Army.