There are dozens of poker rooms in Las Vegas. They can generally be divided into three categories:

Mega Rooms

These are the rooms that have at least 18 tables with live games running literally 24/7. Only a few casinos offer a qualifying poker room:

All of these properties are located on the Las Vegas Strip. From the standpoint of a recreational player looking to play $1/$2 or $2/$5 no-limit, these poker rooms are all more or less the same. Each of them will have seating or a wait list at any hour of the day for those games.

The advantages of playing in the mega rooms are that you rarely have to worry about games dying and are generally dealing with a competent and professional floor staff. These are high class operations frothing with poker action. It's the full Vegas poker experience. You are in a room with dozens of other people all there to do the same thing as you: play poker.

Additionally, the advantage of playing in one of these large poker rooms is that their daily tournaments feature more players and thus a bigger prize pool. While many of the smaller poker rooms in Vegas offer daily tournaments as well, they don't lure nearly as many participants as these larger poker rooms can.

Small Rooms
Most of the tourist casinos in Las Vegas whose name did not appear on the list of mega poker rooms likely have what would be classified as a small poker room. These rooms are characterized as having a dozen or fewer tables and generally very few games running outside of the standard lower-stakes no-limit offerings. If you're hoping to play something other than no-limit hold'em or a higher stakes game, these casinos are not for you.

However, for players looking for lower-stakes no-limit action, any of these casinos will suit your needs just fine as almost all casinos in Vegas have a $1/$2 no-limit game running. You won't quite get the feel of being in a big-time poker atmosphere that the mega rooms can offer, but you will get to play some cards. A few standout poker rooms in Vegas that fit in this category would be:

These rooms can be a great place for novice players to start as they are often small and inviting. It's a good place to get your feet wet amidst a friendly floor staff and relaxed atmosphere if the idea of sitting down in a live poker game seems a little overwhelming.

Locals' Rooms
Scattered around the Las Vegas Valley are what can be referred to as "locals casinos". These casinos are off the beaten path for tourists and tend to mostly only attract people actually living in Las Vegas. Most people making a casual weekend trip to Vegas will never need to bother themselves with these rooms. However, if you're planning on gravitating away from the Strip at some point during your trip, there are a couple of locals poker rooms worth knowing about:

These poker rooms are characteristically full of senior citizens playing ABC poker strategy while grinding out hourly comps. It's pretty easy to find a limit Omaha hi-lo game in these casinos, a favorite of the risk-averse patrons. If you come in with your sunglasses on and start check-raising the locals, you can expect to catch a few disgruntled glances. The locals rooms are an entirely different poker ecosystem than the Strip casinos. There are rarely drunk tourists looking to spew money at 2:00 am in these places.