For me poker converts better but the differences from casino are not very high.
It depends also very much on the brands you promote, there’s much bigger difference in conversion between the brands than between poker and casino.
This is not a simple question because your conversion ratio depends a lot on the quality of the traffic you have going to your site. However, if you assume the same quality of traffic for both I’d say poker. One thing I’ve noticed though is a massive difference in the conversion ratios of the various rooms. For me Pacific has always converted best.