I blitz my way through normal and elite, then explore everything in ultimate.
I explore “everything” probably around the first 10 playthroughs. After that I just focus on all quests.
I just had to do a regearing of my Spellbinder. It turns out, the Mythical equipment was the problem. I needed to switch out to more greens and yellows. I’m using green items with great OA, DA and resists on a couple slots, to make up for the lack of defense on Mythical gear.
I think the poll needs one more option:
I do all the quests and explore here and there. That’s me.
Only the quests which give bags/points/legendaries matter, everything else is completely skippable on the way to the Ultimate endgame.
I read every word in the notes i got and read every word from any NPC,
I think those notes containing history are really interesting
Definitely explore doing all the quests. I usually explore like 90% of the maps, leaving few places unexplored here and there if i know there is nothing in there. Done the leveling through campaign enough times to know where things are 
In every ARPG I touch I have 4 “main toons”
your standard:
- tank & spank
- caster
- assassin (hit in get out)
- ranged
I play this normally, exploring every nook and cranny and overlevelling them if i can by refarming XP rich areas.
All other toons after that are mostly experimental. Those I blitz powerlevel throughout 1st 2 difficulties, and only refarming XP rich areas, if my scaling has fallen off in comparison to the trash mobs.