While some of the groups named are great encoders "AGREED & TESTIFIED" , Your questions a little to broad. There's overall quality Encoders, who max out bit-rates and rip Blurays with all possible subs and TrueHD audio intact. And there's groups who do a fantastic job with compression. Obviously the bigger file-sizes are going to win the "Quality" war. But sometimes, people (and by people i mean mainly me lol) don't want to download a 17gb 1080p release of a b-grade high-school comedy i'm probably only going to watch halfway and realize how bad it is. In all honesty, i'm really digging the teams bringing us more 720p WEBRIPS. Saves a buTTload of bandwidth.

Here are some of the encoders that keep poping up in my downloads. Overall winner i'd say is CtrlHD for consistency, speed, and quality, and the fact they release encodes from 1080p blockbusters to 720p WEBrips/Porn.

Balanced Rips. Size/Quality
ESiR
CtrlHD
DON
HiDt
EbP


Bigger Size/Bit-rate Quality (Mostly internal encoders from hd-torrents)
EuReKA
HDMaNiAcS
HiDt

For Small Size/Compression/Speed of release
SPARKS
AMIABLE
RightSiZE
Japhson
CiNEFiLE

For Tv shows/Webrips
CtrlHD
DIMENSION
IMMERSE
HDCLUB
WEBiOS (Webrip Newboy)

But that's just my opinion, guess it would be different for everyone.