If you're looking for a top poker room online, you're looking at a number of factors: payout rate, ease of play, good interface, and good customer service. The last one should not be underestimated. It is important for a top poker room to have good customer service if something goes wrong with your software or if you are not paid what you are owed. A good online casino will have a 24-hour support operation-- telephone, email or both.
In fact, customer service is a good indication if the online casino is reputable. These days it is easier to set up an online casino that looks on the up and up: it looks as high-tech as other sites. The site may have not been around for very long and does not make good on payments. Check around in online forums to see if there are any complaints about the casino.
If you're looking for a top poker room in a land-based casino, you can use the net to search out the better rooms at Vegas casinos, Atlantic City, or another location. It's not quite as easy to set up a land-based casino as it is an online casino - to the tune of millions of dollars - so you can be pretty certain that a top poker room at a brick and mortar casino will be legitimate .
At a top poker room - whether real or virtual - you'll have the opportunity to play with some of the greatest players in the game, possibly even celebrity players. A top poker room becomes "top" for a reason: it brings in the best players with the most competitive play, and the widest variety of tournament play, sometimes with multi-player games and high payouts.