In pre-222?
I liked the whole Fill/Flex basis of OW.
I got into all the Heroes and all 3 roles, because of that. The ability to just pick whatever was needed for a given situation, was amazing to me. I loved it.
In post-222?
Role incentives & quick Q times.
Honestly, though, i dont enjoy playing Support or Tank, in 222. Being locked into that small of a selection stinks. DPS has more variety, but i dont play it that much in 222 for Q time reasons
In Arcade?
I play Supports in Arcade, because they can do some cool stuff.
For example, Lucio’s Speed is great in CtF, Moira is good in FFA, and most Supports are awesome in TM (Mercy can Rez, like, every 7 seconds. Its great).