Its better IMO to do the quests primarily designed for certain types of chars with exactly those chars.
I mean, really, I wont do Dark brotherhood with my Mage.That would be so fucking stupid, just going in and fucking up everyone with Firewalls-and balls.
Actually...the old guy who's a member of Dark Brotherhood says he despises all the sneaking and daggers from behind or bows from afar and such.
He prefers to just rape the targets and if anyone is around em with his crazy Destruction spells lol. If it fails he just runs away. And (mini spoiler i suppose...nothing really major just some info)
It's far from what it used to be like in Oblivion and they have basically abandoned the Tenets and old attitude and not every mission needs to be finished unseen or whatever.
So imo mage is the most flexible class. Can basically enter any faction without ''breaking RP''.
Except perhaps Thiefs guild. But if you got good alteration you can use Invisibility spells and Open lock spells and such.