Ummmm, I'd be THRILLED with either butt! I am an apple shape with no butt. I liken it to a potato with toothpicks sticking out... I have hated that fact for years, but with exercising I've started to see a tiny butt back there. LOL I will always be larger up top no matter what - I just have to become okay with that... someday. Or, I could get butt implants - do they do hip implants as well?
I'm a fan of the first butt, too. Both are nice,just different, and I think genetics has more to do with it that almost anything. Lunges, squats, and dead lifts are all great ideas for getting some lift and nipping in the thighs, but so much of it is just how we are programmed to put on fat. You may just carry more flesh in your rear, and that's okay
I do martial arts, and do lots of kicking, squats, lunges (have been training for 5 years now), and still genetics dictates that I have a flat butt (flat across the bottom line)
I think both butts are fairly similar, its just the swimsuit and tan that makes the second look more toned! and I would take either any day .. LOL
I'll admit I don't see much difference between the two aside from a few lbs and a tan. I'd take either at this point. I have a HUGE butt which never bothered me until I became so overweight. It's "hangy" I think and I can actually feel the weight pulling on my back. I'd just like it to be smaller and more firm than it was when I was thin the last time. I like having a big butt...just not so saggy looking.
I also think they look similar, the first one just has higher body fat and possibly different bone structure. The second chick looks like she is small boned, the other might be more medium/large boned.
Another butt/lower back exercise: Superwoman. Lie facedown with your arms and legs stretched outward, then draw them closer toward each other while squeezing your glutes. If you go to the Women's Health mag website and search "superwoman," there's a link to a diagram and some alternative versions. It's not as easy as it looks!
To answer your question: put on the same bikini bottom! The butts, to me, look the same. You should be pleased to be blessed with your bottom!
The exercise suggestions are correct in that they target the glutes, lower back and hammies but keep in mind that, like with any type of ab work, you will be strengthening the muscle underneath the fat. We all have six packs underneath. We all have awesome butts underneath, too. Without fat loss, your butt may get bigger because of the muscle growth.
Also, I want to note, like others already said, genetics play a role, too. I have 15% body fat at age 41. I have always had stretch marks on my hips (from puberty) and a tiny bit of cellulite on my buttocks. Genetics gave them to me and no amount of exercise will change it. Luckily, I understand that and just don't care.
Hopefully, you can learn to love your shape, and whatever genetics you have and let it go.