I don't know, apart from poker, the options of B, well apart from Monopoly but I didn't know you could play in the casino as well. I suppose the best thing would be to have both options mixed in the casino and try them out, but if I had to choose one I would go for B, because in PVP games you can win in the long run if you are better than your opponents.
For me, I believe slot games are much better, as they are more entertaining, have less pressure & stress, and gives you the chance to turn small bet into a large chunk of money.
Yes, the good thing about them is that you don't have to think, you spin it and see what comes out. That's what I've been playing the most lately.