What Makes the Best Online Poker Software?

There are plenty of online poker options available today, but not all of them offer the same experience.

In your opinion, what is the best online poker software currently available? What features keep you using it, and what separates it from the competition?

I think the Best Online Poker Software is the one that balances stability, player traffic, and a clean interface. A good selection of games and smooth gameplay are what keep me coming back.