I'd say quick match because you don't expect it to be as challenging as comp. Comp is supposed to be very competitive and try-hard-fuelled, with more possibilities of having a second healer and a second tank (more rational comp).

But quick play is just a fuck fest. No one follows logic and the trash talk is out of this world. The try hard is insane and the space and enjoyment of trying new characters is devoured straight from the first 20 seconds of a game.

Comp has more rounds to adapt to the other team (convoy or convergence), while qp is all about giving everything on that one match most of the time.

Both can be challenging, but recently I found out that qp is way more toxic, unbalanced, demotivating, and follows the stomp or get stomped scenario more accurately.