I would choose a site that offers plenty of free-rolls they are a long slog but it gives you plenty of practice without costing you a fortune.
Poker King does a free-roll every 3 hours and change formats from NLHE and PLO depending on the day so you get practice in both games.
pokerstars are perhaps the biggest online
poker site and the free-rolls are limited to areas and depends on Passwords and tickets so you are lucky if you can play more than 2 or 3 a day.
Also being the Biggest means there are more players, I have seen 10,000 in some.