Stockfish 8, Komodo 11, or Houdini 5?

@janosopeligroso yes, about 30-40 elo.

Unless you are Magnus Carlsen I don't think you'll ever need anything more than Stockfish 8.

The problem is that SF8 is half a year old.

Better use latest development version, its simply newer.

Here you can see the difference in relative strength increase since version 8.

nextchessmove.com/dev-builds

I heard Komodo is the best in closed positions where only slow progress is possible, Houdini is the best in tactical positions and Stockfish is very good in handling positions with imbalances in material. Anyway I don't think there is any difference what engine to use if you are below the Grandmaster level. So just use the latest Stockfish, cause it's free. It is debatable anyway if the move engine suggests is really the best, but for just knowing which moves are ok and which are flawed all engines should be equally good. And they are also equally bad in explaining the reasons behind these moves :)

I'm loving StockFish 8! Having used Houdini 2 for a couple of years, SF8 seems to find better and sharper solutions.
Is there a version better than SF8? What is SF8 rated btw? 3490?

stockfish 8 rules like a chipmonk.

This site shows you the top engines on the market:
http://www.computerchess.org.uk/ccrl/4040/

FIDE doesn't have a rating for engines, so the question about SF rating is irrelevant. However, CCRL ratings show how different engines compare to each other. (But they are not equivalent to FIDE.)

There are too few games between humans and engines and it is only known that the best engines are much stronger than humans today and usually draw or win Grandmasters being a pawn or two down at the beginning.

CCRL and IPON (http://inwoba.de/ ) are good in general but the problem is they don't have the latest version of Stockfish, which is now considerably stronger than stable Stockfish 8 from 9 months ago. There is also an assembler version of Stockfish (yeah, the full Stockfish rewritten in ASM), called ASMFish, which is faster and therefore also stronger. There are some results here (http://spcc.beepworld.de/long-thinkingtime.htm ). They say the latest ASMfish is nearly 80 ELO ahead of Komodo, but this can be somehow biased, cause the tester is connected with Stockfish devs. Also note that Komodo scales better than Stockfish for longer time controls and more cores in processor.