For me Stevie Nicks gets the slight edge over Heart of Glass era Debbie Harry, with roller skating era Linda Rondstadt a distant third.
For hottest but obscure, Sonja Kristina of Curved Air (obscure in the US anyway).
When Heart debuted in 1976, I thought Ann and Nancy Wilson were both pretty hot.
Stevie Nicks. Absolutely.
[sub]Unless I think of someone hotter…[/sub]
Here’s a great clip of Stevie at her hottest/highest, backing Bob Welch at the 1978 California Jam.
Joan Jett. Her solo career didn’t pick up until the 80s, but she was in the Runaways during the 70s, so she counts.
Well, in '79-80 my roommate and I sent a letter to Chrissie Hynde, asking if she minded if we formed a religion based on her…
Simply because I respect her has a songwriter, singer and a bandmember (to me, she was the first “rocker chick” who clearly wanted to be seen as one of the band first - and she totally pulled it off, IMHO).
But…damn! She is all kinds of Hot - she clearly grew her bangs out to take attention to her beauty. I remember seeing a high school photo in Rolling Stone one time (just looked; couldn’t Google it easily) and thinking - whoa! And then I saw this photo of her and some other punk rock girls at Malcolm McLaren’s shop SEX - it’s a photo from behind and Chrissie is wearing some sort of Playboy Girl type of outfit - just beautiful legs.
I’ll be in my bunk.
Oh - and yeah, Stevie is amazing, as is Debbie Harry and the Wilsons - absolutely no argument from me. Nancy is another truly great guitarist (mostly rhythm) who deserves to be considered simply as a guitarist in her own right, just like Chrissie…
Let’s not forget Andrea True. How many women can you name who had a top 5 record and are still better known for their career in porn?
If Joan Jett counts she’s got my vote. Not only could she kick crap out of me, but she’d do it with a smirk on her face. There’s something sexy about that.
Yeah but that was early 70’s era porn where the women weren’t exactly known for their good looks 
I’d second Sonja!
Curved Air are one of the groups I most regret not seeing live…
Stevie Nicks. Or maybe Pat Benatar. (I loves me a redhead.)
Siouxsie Sioux. She became really big in the 80’s but Siouxsie and the Banshees did debut in the 70’s. That woman is still super hot.
OK, this one is like one year outside the 70s, but Kim Wilde was pretty cute.
But I noticed that she has a website currently, and I have to say that oh, yeah, I’d definitely hit that .
The book that has the photo of Chrissie Hynde at SEX also has a great photo of Siouxsie from before she formed the band and was just a super-extreme punked out club goer. In the photo I am thinking of, she is topless at a club, well, just to be outrageous…
The book is called PUNK! and published by DK - a very UK-centric view of the punk scene - I think it is a collection of punk-related magazine articles from that era, with a bunch of new photos - two of which I seem to like very much!
Annie Haslam. Then Stevie. Or maybe a sandwich…
Or, if you like your rock a little more countryfied, there’s the 1970’sDolly Parton
Depending on your definition of “rocker” I’ll throw these names in the hat…
Olivia Newton-John
The ABBA chicks
Another vote for Joan Jett. She looked great in the 70s. She looks great today. She looked great blonde (my husband took that photo). She even looked great bald.
Linda Ronstadt. See, I’m a girl, and my definition of hotness was wanting to be Linda Ronstadt. Prisoner in Disguise era, maybe. I even started wearing silver bangles and hoop earrings, my hair long so I could put it up, jeans and hippie blouses. A lot of that style is still with me to this day. I thought she was hot.