Perfect at any weight ...
Proportion is key.
I tend to prefer women of hourglass and apple shapes because any added weight goes into their bust and hips. The great majority of women (80%+) are straight or pear shaped so it either goes equally into all portions, or more into their ass (not always so well either), well before their breasts.
When
I authored most of the structure of the current layout of the Wikipedia article Female Body Shape, it was the first time anyone had take this technical approach. I cited several studies, and others have as well. Those first three sections today still remain largely unchanged, because they are the reality of the female curvature.
The best indicator,
far better than BMI, is how much a woman's stomach overhangs. It means how much of her body can distribute weight, and how much it cannot. An inch (2.5cm) or less free-hang when standing is considered healthy enough. Typically this means a woman some 20-30lbs. beyond her most fit and ideal.
Also remember that women who exit their teens, as well as endure any pregnancy, tend to change radically. I mean, they lose some bone mass, they often widen in structure, and some of that -- regardless of diet and exercise -- never comes back.
One of my favorite examples of just the teenage to womanly changes is Kate Dillon. At age 16 she was a size 6 and considered to be the next Cindy Crawford. But once she hit 18, she had to starve herself to maintain her size. By age 19, it became a serious threat to her health.
She eventually came to grips with the reality that she was fuller figured, +2-4" on her hips and chest from the alleged "average" of her size. She's not healthy below a size 10 at all. Now she does hover around a size 14 normally, which means she's not as thin as she can be, and maybe 20-30lbs. beyond her most ideal.
So what? Many men are turned on my womanly curves. Director Josh Weadon is known in Hollywood for requiring women to gain 20lbs. or so for more "feminine" beauty on-camera, and his shows and the women he shows off on them tend to be very, very popular as a result.
Now I won't deny that Carmella is beyond healthy, as she has more than an inch on that stomach. Carmela also wasn't a perfect hourglass, having an enhancement and probably be a tad more straight with a pear-tendency, but she was still curvy with a good inflection. In any case I'd become one with her and enjoy her full form as she's still the same, curvy base and looks good regardless.
Sometimes women are "ideal at any weight" or at least to a point.
Autumn-Jade is one of my absolute favorites, as her body bulged and plumped out, while she still didn't have much of a gut. Kerry Marie was able to take on +50lbs. before she finally started packing it in her stomach. Women like Terry Nova and Karina Hart have unreal hourglass figures, while soft-bodied, but not remotely fat at all. And Chloe Vevrier has been eternally beautiful and curvy, taking on two kids has only made her more womanly. Probably the ultimate I've ever seen in a hourglass is Michelle Bond, who was thinner in her earlier 20s, but filled out like a venus into her 30s, and is only getting more curvy, fuller and hotter, without being remotely fat or packing anything in her stomach.
I don't like many BBWs at all, but Maria Moore is my deepest desire. Laura Orsolya was more of the same, although she finally hit a size that put more into her stomach more recently. I can talk about models who look good, and you'll get me lusting after "packed, but slender" FFWs like Chloe, Karina and Terry. But when it comes to the sack, I'll bed an oversized, but proportional, lover that is even bigger, and enjoy her the most.
And that's before I even hit on the apples. Apples tend to always have a bigger chest and bust than their stomach. My wife 5'3" apple wife has varied from as small as a size 6 at 125 lbs. to close to a size 20 at 200lbs., a 38-24-34 to a 42-28-38", and her breasts just enlarge before anything else (although at 175-200lbs. her stomach does become noticeable over her hips, and not healthy at all).
The one thing I love about being a man is to enjoy a woman through all her cycles. The second I hit 18 I started sleeping with women in their 30s and 40s as I loved their softening and widening bodies. I met my wife when she was 18 and have been laying with her and her alone ever since. Now that she is into her mid 30s, she's only gettig more beautiful. Yeah, there's something about a young woman who is pert and not as soft. But when it comes to a woman and her natural cycle, with age and softening comes something far more erotic.