I don't use them since i don't speedrun and play rather casually. I like to read stories and be a part of them. In general my recommendations would the the less addiction to addons you have the better. The game should be played like blizzard meant it to. I do know that there is a bunch of essential addons you really need to have one.
I am definitely in the do not use camp. Back in the day, I used quest helper addons. At first, I was please with the convenience, but after a while questing just seemed more like a chore than, well, a quest. Instead of listening to an NPCs story and trying to figure out how to help, everything was done for me. It took out all the adventure. After blizzard integrated a quest helper, I would disable it. But it came to a point that some quest text wouldn't give any information about locations, and you were required to use the quest map to find it. IMO, after that WoW stopped being an RPG and just became a G.
But to each his own. I just don't want the writing to require a quest helper, since I prefer not to have one.
Using websites like Thottbot just like back then for every quest is the way to go. But if I get too lazy then I will just get a quest addon while still reading through and follow along with the stories.
I'm sort of a weird split... I'd prefer if there were no addons. However, I will use any and all addons that give me any advantage. So if questie is available, despite the fact that I am familiar with the content, I will use it. I'd probably quit if Blizz implemented LFR (I know they wont) but if someone makes OQueue group finder available (this is an LFG/LFR addon) I will download it immediately and use it begrudgingly. I will complain about this but simultaneously contribute to the problem by using the addon.
I won't be using a quest addon, but I will probably use a leveling guide. I don't care much about questing, but I want to avoid the retail experience of easy-mode, run-to-the-map-marker style of doing things. The leveling guide will mostly just be for efficiency, so that I pick up the right quests, at the right time before going into an instance or new zone. I don't want to run back and forth a zillion times or miss picking up important quests/quest-lines.
I secretly hope the addon API allows something like Storyline but it's a long shot. I won't use a questhelper type addon though.
I'd like to be a purist and not use a mod like that... if I was single and had no aspirations of a job or family.
Unfortunately I kinda like my family which needs me to keep the job which forces me to make changes to things I love so I can still fit them in.
I will be conceding and using a quest helper to reduce wasted time in-game when I do get to play between responsibilities.
I'm lucky, the fiance wants to play as well and we don't have kids yet.