It depends on the games. If you got a game that'll go for a good amount of money and it's in good condition (say, Marvel vs Capcom 2) then sell that individually. Now, on the other hand, if you have a bunch of crap games then it'll be better to sell them in a lot just to get rid of them. The best thing to do would be to search eBay for each game you're selling to see what they generally go for and then decide from there if they're worth selling individually or if you should just throw them in a lot with a couple other good games.