Pay-to-Play Games
World of Warcraft-Huge player base,mix or old and young players.Mostly solo till level 20, groups are varied by server.
Everquest-medium player base, mostly older players.Mostly Solo till higher levels, lots of groups in upper levels.
Runescape- medium player base, mostly younger players.Mostly Solo, little to no group activities.
Dungeons & Dragons Unlimited- medium player base , mix of old and young players.Mostly solo,till after the tutorial. Grouping is slow.Pay to unlock all classes and races. More island/worlds to explore.