Best place to play right now is CoinPoker. Has quite the range of limits and hundreds of players on at all times so far.
America's cardroom would be second on my list. It takes 3-5+ days usually to cashout though and you never know what bitcoin rate you're getting.
Nitrogen Sports probably third. SWC next, but would be higher if it had more players.
BetKing is new and I haven't seen any games whatsoever, so I'm not sure why it's being recommended. It could turn out to be good though if it picks up, but noone knows.
The big problem with CoinPoker is that you are not really playing with bitcoins, you play with CHP tokens, so you are also open to manipulations in CHP, you are actually also investing in this token while playing and that's why I would avoid playing.
You have America's card room, thousends of players available, that's the best in my list because the site is not just closed for bitcoin/crypto players, it is open for all the kind of players and they also accept fiat deposits, which means that there are players all the time, and even if the crypto market suffers from downtrends/ people run away from crypto, there are still going to be players at that site and you would still be able to play with bitcoins.
ACR the only poker room service that i play so far , trusted and comfortable. The other mostly can't survive run this kind pvp game, it has low interest here in crypto community , so not much choice when it comes to bitcoin poker room. Betcoin ag it's shady , I wouldn't recommend it.