It was either Bioman or Flashman, but I'm not sure which. They both have round-ish helmets, so Lil' baby Angel thought they were the same show for the longest time. :1 I'm inclined to say it was Flashman though, 'cause it's the one I remembered more of between the two.

Mine was Zyuranger, and I just finished watching the show on Shout Factory TV online.

Gokaiger. Still my favourite.

Zyuranger randomly on a whim because I wanted to see the show Power Rangers came from.

I was never even into Power Rangers, much less MMPR (since, you know, I was born in 1996)

In general, Megaranger was the first show I watched a full episode, as for a while I'd watch the first few bits to see the openings and get a feel. In terms of completion, Hurricanger.

In full? Zyuohger. Fun times.

Bioman, when it originally aired in the Philippines with English Dub. I was like 6 at the time. It was looking for this show again that led me to start watching Sentai as an adult. I even had the pleasure to be part of the GUIS team that completed the translation of the series.

Mine was Goseiger. It’s a miracle I’m still here.

I'm gonna one-up you on that.
While my first Sentai was Gokaiger... the first Sentai thing I watched period was Super Hero Taisen.