Personally, I prefer, small hole (mine was drilled for std pin, so installation was about 10 mins), raised mag fence like on my Colt Sporter Match HBAR Model R6601. Sold the non-bayonet lug upper and installed a complete including bayo lug A2 Colt 20" upper. If I have to, the damn internal black can be professionally removed for about $200 by a gunsmith.
Now, when I had an R6600 AR15A2 HBAR, mag fence was not an option, push pin was an after market pin with a small ball bearing, but it did have a bayo lug, and NO internal block.
So I traded that slab sided rifle for a Pre-ban Bushmaster which now has two (2) A2 uppers, both with 20" Colt 1/7 barrels (1 HBAR, 1 A2).