just gonna throw the "use the search function" statement in before 3 other people do.

but anyhoo to answer ur question, leveling more than 1 character at a time will ALWAYS be slower than leveling 1 by itself. whatever xp u get from kills is split 2 ways, 3 ways, or however many ways depending on how many characters ur doing. however, if u have 3 or more grouped together, you get a slight bit of "group xp" which is nice, but it isn't enough to make up for that xp-split.

so basically, just strap in, hold on tight........and get ready for a slow walk to 70 =D



edit: also if u can, avoid collection quests. especially if u are doing 3 or more characters, collection quests can be hell. that might speed up your leveling a bit.