This does NOT portray my feelings on who's the hottest girl in my mind. In fact, I have a different list for my selected hotties.
1. Yuuri/Time Pink (Mirai Sentai Timeranger)
Well, what can I say about Yuuri. Considering that many people of the new millenia started the Sentai series in either Dekaranger, or this... They held her quite highly in attractiveness. It also helps that she is one of the few girls that take actual team leadership, and is a Tsundere, a popular character archetype. This probably contributes on why people consider her hot.
2. Nanami Nono/Hurricane Blue (Ninpuu Sentai Hurricaneger)
I... really haven't touched Hurricaneger at all. But, just one name from it would instill instant squee: Nanami Nono AKA Hurricane Blue. It's mostly thanks to her actress, Nao Nagasawa, who's quite popular amongst the fandom, and yes... I do have to admit that she's really pretty.
3. Marika 'Jasmine' Reimon/Deka Yellow (Tokusou Sentai Dekaranger)
4. Sakura Nishinori/Bouken Pink (GoGo Sentai Boukenger)
This is also one of the great candidates of hottest Sentai babe ever. I mean, not only Haruka Suenaga (Sakura's actress) is REALLY a looker, she also gives a good portrayal of Sakura, a twist on the usually girly Pink Sentai warriors: tough as nails instead of cute and feminime, though she has some cute moments and when that happens, Haruka Suenaga usually makes that REALLY adorable.
5. Miu Sutou/Go-On Silver (Engine Sentai Go-Onger)
This is also one of the more popular choices of hottest Sentai babes. Miu gets her credit of hotness not just on her contrast towards the Go-ongers (more serious personality), or her actress (Yumi Sugimoto), but also the fact that she takes lessons in Tsundere department from Yuuri, making her much more hot in the eyes of fans.
I would add the Shinkenger, but right now I can't decide who qualifies more; Mako or Kotoha, both of them has quite the competiting fanbase that I can't pick both of them. We'll see. Also, I almost considered Mele from Gekiranger; but since she started out as a villainess, which means by default she gets her sexy wear, she's written out from this observation.
So anyway, that's my report on who are the most commonly revered as 'Hottest Sentai babe' as of today. And if you want me to do the 'cutest' instead? Well, I'll wait until later.
And this is just my observation, so there may be... mistakes. Correct me if I'm wrong. I'll see ya later!