Meditation FAR surpasses focus for mana regeneration, especially considering the ability to actively meditate. But like both of the above posters mentioned it is not a natural fit for a caster using mysticism as much as focus.
Honestly the MR you get from focus is pretty weak, and the main reason you need it is to strengthen all of your mystic spells, including the strength of your rising colossus. It would be like evaluate intelligence offering a small amount of mana regeneration, a nice perk but not a game changer.
I just didnt want anyone reading this thread to think focus was definitely the way to go, meditation > focus, unless you have a mystic. Then both if possible, lol! Or none, with enough MR on the suit, or the capability to use wraith form you can do pretty well without either!!
--edit--
Its also worth mentioning meditation of at least GM skill gives a bonus to the rate at which the MR on your suit regenerates mana. Ive got a char with 90 and use either the shaman staff or a spell book to put it at 100 and can definitely see the difference.