I gotta be honest I think I much prefer Once A Ranger. Forever Red is good, but Once A Ranger was a pretty awesome celebration as well. Even with Operation Overdrive being the joke that it was, that 2-parter is still just stupid fun. Legendary Battle isn't even in contention it's such an abysmal train-wreck of missed opportunities and failed execution.

The order for me goes:
Forever Red, for being freaking badass.
Once a Ranger- It lasted longer than two minutes, and, for all its faults, it's still better than...
Legendary Battle (Heck, most of Super Megaforce)

I really loved Forever Red, but I have to go with Once a Ranger. It really made NOverdrive bearable for me. Plus, Bridge Carson. 'Nuf said.

"Is it...buttery?"
"The butteriest, sir."

100 x times better than the Legendary Battle, that's for sure.

Forever Red