If you were only able to pick up ONE addOn...

[Heratix]

GRID 100%. All other add-ons are just to pretty up the interface for me :P.

[Cayumi]

If I could have only one addon then i'd learn to live with SpartanUI.

[Contri]

Clique , can use blizz's UI too heal.

[milowen]

Macaroon.

[Failsauce]

Vuhdo for healing

DBM for tanking/dps

[Zeerus]

Bartender.
And to the person that said Spartan UI. I don't think that counts, because that is like 20 add-ons. >_<

[Korgash]

DBM :]

[ennui]

Peggle, of course.

[Fenixdown]

DBM. Everything else is basically covered in some capacity in the standard UI.

[Endler89]

GearScore

An addon that just makes it so you don't have to inspect someone. Waste of your addon. If your pugs only work now because of gearscore your running with a fail raid leader. Good raid leaders don't use gearscore they inspect on their own and can tell fails by inspecting gear/gems/talents/enchants.

I raid lead so it would be btwn dbm and recount. I'd lean recount because i can check raid performance to see who failed on what in a given fight.

[Xuany]

I play two healers religiously so, this is hard, either Clique or Grid and it will probably be Clique rolling with default raid frames.

[Manchaku]

Peggle or Icehud

[Screwtape]

Add-on that I would be most scared of not having? Omen.
Add-on that probably helps me the most? Recount.

Sure you could use WoL of whatever, but Recount is much less cumbersome and you can see what's going on in the middle of the fight. Because when you're a DPS, if you're not getting better, you're getting worse.

[Deleted]

Bartender when not raiding (I hate standard UI).
DBM when raiding.

[Deleted]

For tanking, DBM and omen threat meter

for heal, Quartz all the way, im druid, so watching my HoTs is like....cake

[Archet]

I would have to say Pitbull

[proto]

Grid 8)

[Kogu]

KillStreak


makes my pvp more fun

[Bowz]

bartender

[Lucifra]

dbm for me