I know Gotham isn't on The CW. I'm off and on about Supergirl. It's extremely tonally similar to Flash, so I get worn out watching both. I'm giving it a fresh chance with its CW season though.
The removal of a certain character from Arrow has greatly improved the show the last few episodes.
That said I'd go:
1. Flash
2. Legends
3. Arrow
I don't watch Supergirl, Gotham, or iZombie (haven't heard if it). If they do a Crisis and merge Supergirl I'll start watching it. But I'll watch the crossovers at least.
I know Gotham isn't on The CW. I'm off and on about Supergirl. It's extremely tonally similar to Flash, so I get worn out watching both. I'm giving it a fresh chance with its CW season though.
Huh? Flash, despite some weird missteps here and there, is still a ton of fun. Arrow has become a total trainwreck since the crossover, and I say that as someone who generally did not have a problem with S3 as it was airing (though, in hindsight, it really wasn't good).
The Brave and the Bold was better than Flash vs. Arrow. Boomerang trumps Rainbow Raider.
Legends of Yesterday was better than Legends of Today. Started Savage versus finishing Savage, in which case the latter wins.