Zhaomal would probably say all, seeing as he seems to be almost maxed in all of them. And getting filthy rich teaching others some of it.
I would say that all Ways have their uses, together with pros and cons. And also you might have gotten a more unified answer if you asked what is the best offensive/defensive Way.
I like to look at them in this order with the current spells (offensive -> defensive):
DW -
RW -
CW -
AW -
BrW -
BlWI'm also agreeing with Mekora and Mishka here. Let your character suit up in an unmistakenly magical direction
The ones among us who have played a few RPG games, be it Oblivion or online stuff, have always seen Hunter/Ranger chars summon creatures to aid them (BrW implementations?). And Healer chars kinda need CW to heal. RW is a nice Way for blacksmiths and crafters.
My personal fav. while playing gotta be DW. I still remember the somewhat sadistic fun of regenerating your own HP by taking it from monsters.