[Matrixbeast]

I'd definitely have to say,
5. Titan Megazord. An awesome look, a nice combination, and a pretty cool alternate form. I don't even have the weapons for mine (And Garuda's wing is broken) and I still love it!
4. Legacy/2010 Megazord. I know it doesn't have the best reputation, but I just adore mine. Yeah, it's not as big, and yeah, the figures were simplified (No moving wheels and the Triceratops's tail doesn't unfold), but it's a great representation of the original (Or replacement for those who never had one *Cries*)
3. Alien Ranger Battle Borgs. For a time, until I got my first Bionicle, my Black Frog Battle Borg was the most articulated toy I had ever owned as a kid. It was awesome. While I wanted either the red or while one, I settled for it, and I'm glad I did.
2. Thunder Megazord. The Red Dragon is awesome alone. I remember my brother and I both owned one because we couldn't share it because it was so awesome. The armor it got just made it even cooler. I loved the Thunderzords, and they're awesome PR toys.
1. Mega Voyager. The toy is so awesome. The combination was something that blew my 10 year old mind. The weapon not being a giant sword was jaw dropping to me, and the design is just beautiful~

Honorable mentions go to Ninja Megazord (I love it, but it's painfully basic and nothing I'd consider "Must have"), the MMPR Figuarts (Which I just didn't feel like listing), and the SWAT Megazord (Which I never owned, so I'm not certain on it).