Wow. Supergirl and Power Girl have the worst Nightwing And Flamebird costumes. They're extremely busy and armory and I don't like the masks/helmets. They're also extremely samey from each other
Superman & Jimmy's original looks are classic style comic outfits which are great. Van-Zee and Ak-Var wear the exact same outfits so let's skip them.
I actually REALLY like the Return to Krypton Superman & Lois versions though I prefer the interior art.
Chris and Thara Ak-Var's first costume is a great modernization of the originals I feel.
Their 2nd costume is basically a good version of the arnored look due to the simplicity and having more color
Their 3rd costumes are the ones I've seen the most but tbh i think they're tied with the armored look. There's some characters or aliases that I prefer not looking like the most known member of the group (they look too derivative of superman and nightwing and Flamebird shouldn't imo)
Dick Grayson never had a bad nightwing costume. His worst suit is probably the 90s glider one or his captain america one.
Tbh even Cheyenne Freemon, the Nightwings, and Nite-Wing have good costumes. (To be fair 4 of those basically use Dick's old ones)
Bette Kane also has good Flamebird costumes