I like Pragmatic, for me it's one of the best!
Well, the OP is asking for your opinion so it is ok if you consider it the best site and others not. What would be nice is to have some ideas around why do you consider that site your choice. I value above all reputation and honesty in the processes and money handling, then the variety of games and how easy is to get involved in new games. Lastly, usability is also important.
They have colorful and enjoyable games. The most popular games you can find on the Internet are Sweet Bonanza and Gate of Olympus, which have many cool features, such as choosing the volatility! Many new players started from their games!