New Campaign

I want to buy the Factions campaign but I was wondering if it would be better for me to finish all the missions on the Prophecies campaign first?

Well, there's no real penalty for buying it now or later, it doesn't matter.
If anything, I suggest buying factions now, to atleast have some more skills at your disposal.

(Ofcourse, if you're a person that likes to finish stuff, then by all means, finish it first.)

my personal opinion is that it's best to finish a campaign with at least one char before starting a new one.... but that's just me

Well, the only real thing I was worrying about was that if I don't finish the missions on Prophecies and start missions on Factions I'll have a big space in the story =/

There won't be a space in the story as factions is a separate story to Prophecies. The only gap you'd get is the memory gap between where you left prophecies and when you finally come back to it...

Ah, ok, thanks everyone for your help. I'll get Factions ASAP.
=]