Really? I've thought Season 4 of Arrow has been stronger than Season 2 of Flash, noticeably since they returned from their midseason break.
My personal list (this year) would be:
1. iZombie
2. Gotham
3. Arrow
4. Flash
5. Legends of Tomorrow
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.