IPON is the best rating list for comparing the strongest chess engines. The rating list is generated and maintained by Ingo Bauer. He is normally quick to test new engines or new version of engines that might be among the top 20 strongest engines.
Conditions
Ponder : ON
CPU : 3.2 GHz Phenom2 (x6)
Operating system : XP-64
Cores : All Engines with 1 core
Hash : 256 MB
Table-/Shredder-/Bitbases : 4 pieces
Cache for Tbs : 64 MB
Time control : 5 min/game + 3 sec/move (mean game length ~ 16 Minutes)
Openings : 75 different opening positions (no books) (50 positions before 2012.01.28)
Positions : Changing colors (150 games engine vs engine)
Learning : OFF
Pros
Each engine is tested under the same conditions. By focusing on the top tier of engines, Ingo is able to generate statistically significant results for a new engine/new version before any other rating list can.
Cons
Only the top tier engines are tested. The games are not shared with the public, meaning that Ingo's results must be accepted on faith.