MarviG said:
http://dragonage.wikia.com/wiki/Main_quests_(Origins)#Ideal_orderModifier_Ideal_order_.28section.29
Wow.... this is exactly how I did them on my first play through.
OT: I second the Orzimmar last idea. Do it dead last when you should be able to breeze through the enemies. Everyone else seemed to think it took forever, whereas I found it the shortest part.
I also enjoyed it a bunch because I'd picked the Dwarven Noble origin and I liked the idea of returning home as a powerful grey warden.
Also, don't play mage your first time through. I found mage the boringest playthrough.
Mind you I've not played through as an archer and apparently that's the most horrible experience available.
I liked the circle part so it mightn't suck for you. But I will say that I don't recall my time there as a mage, but enjoyed the time there as a warrior and rouge... maybe that means it's a second option for you if you're looking at mage (based on the fact that you are chasing the spirit warrior spec)
EDIT: Actually someone mentioned Shale, and I noticed that you mentioned DLC. Do shale straight out of Lothering. Do return to Ostagar when your tank is about lvl 10 otherwise you'll get items there that you may be unable to use for a little while.
So:
Origin,
All mandatory starting quests,
Shale,
Circle/Elves,
Elves/Circle,
Ostagar,
Arl o' Redcliff,
Warden's keep,
Sacred Ashes,
Denerim (You'll possibly be popping in and out throughout the game anyway),
Ostagar/Deeproads,
Landsmeet