I'm really torn on this and playtesting hasn't resulted in a clear answer for me yet.

I'm having a hard time figuring out what my mana regen actually is in combat.

How much magika regen do you get at base? Are all of the regen bonuses additive? etc etc

Does anyone have hard numbers on this?

It also seems that if you have a spelled queued to cast you dont' regen while holding the spell. I can see not regenning the mana for that spell, but if you were below 100% the other mana should still regen right?

Anyone shed some light/thoughts on this?

More Magicka because I don't think regen actually regenates magicka if your channeling a spell

a balance of the both is the best. You'll need to focus alot into max-magicka anyhow to cast powerful spells with rapid succession.

Yeah, I think this is the best approach. What I do is I wear robes that increase magicka regeneration. Early on they increased regen 50%, now it's 75%, later who knows (not me). When I level up, since I am playing a mage/archer/backstabber type I increase magicka 4 times then health 1 time and ignore stamina. This seems to result in a workable balance of magicka amount and regen.