Inside - more
The Edimax EW-7711ULC is Mediatek-based, has a bent-metal antenna and Skyworks SKY85703-11 5 GHz front end. This Skyworks part has both a 5 GHz transmit power amp and 5 GHz low-noise amp (LNA) for boosting receive signals.
Edimax EW-7711ULC board
Like the Buffalo, the Edimax EW-7811UTC uses a formed-metal antenna and has no external amplifiers.
Edimax EW-7811UTC board
The Linksys AE6000 is MediaTek based, uses a bent metal antenna and, according to WikiDevi, uses an RFMD RFFM4501 802.11a/b/g/n/ac WLAN Front End Module that includes both 5 GHz transmit power and LNA.
Linksys AE6000 board
Swapping back over to a Realtek-based adapter, NETGEAR's A6100 looks very similar to Buffalo's WI-U2-433DM
NETGEAR A6100 board
This photo of TP-LINK's Archer T2U isn't very helpful since there aren't any shots of the naked board. So I'm taking WikiDevi's guess that it is MediaTek MT7610U based. Its antenna looks like it uses both bent metal and printed circuit.
TP-LINK Archer T2U board
The TRENDnet TEW-804UB gets the prize for largest antenna. But like all other Realtek designs, has no external power or low-noise amplifiers.