The official one, which runs great. And since it's all open JS there's even alternative app menus and launchers if you're not happy with the stock option
I forgot to add that this LCD screen is perfectly readable in direct sunlight, I wouldn't know it was not e-ink at a casual glance. Even at extreme angles the only thing that makes it difficult is the reflectivity of the front glass, but I have a large font watchface so even that is a minimal issue.
