Out of four responses to my Reddit post, Suprnova is the slight favorite.
Suprnova - 3 mentions and 3 people using
Flypool - 2 mentions, 1 person using, others warned to stay away because of Flypool's possible dominance/size
Slushpool - 1 mention, 1 person using
Dwarfpool - 1 mention, 1 person using (me)