Depends what country you are in. As a U.S. player, I am unable to play on Pokerstars and 888poker.
Ignition Poker is so small on my computer screen, I prefer not to play there.
intertops gets my business, but I have not seen any growth there. I play some at America's Cardroom, or one of their many skins, which I think over the years I have played on 11 of them. That leaves BetOnline as the only other reputable place I am able to play that I have some confidence in getting paid. I can't say I trust getting paid at Bet Online, I am almost at an amount that I will try a withdraw to test how reliable the withdrawal process goes there. I know I got one poker site to take care of my withdrawal that almost made my head spin, but I had to resort to letting them know I would have to relay to my poker forums that they were a no pay poker site.
P.S. I guess Carbon, Sportsbetting.ag, and their skins may be another one to look into, their payout ability is reliable.