this will be an in-depth situational answer.
if the game recently released then preferably a dps that can offtank/offheal and focus on the tank / heal part until i have enough resources to focus on dps, this is to ensure i get into dungeons, dps queues are a pain,
if no off-class options then its a coinflip for heal or tank unless i know i got someone to fill that for me.
(most often not)
if the game is thriving with no queue issues :
i'll pick whatever class can deal damage with a polearm ; if none,
i'll pick whichever class has the most movement options, (typically rogue dex stack / agi stack dps i guess)
(i feel like s&s+gs had the most mobility in throne and liberty though~)
i guess i really dont care what role i fill aslong as i can displace either my enemies's position or my own alot, or i have a sick polearm.
that said, my wow comfort pick is warlock ✌️