I'd buy that '72 and drive the crap out of it!
And I wouldn't say I'm particularly biased to the '72 body style, since I actually intend to hang '71 sheetmetal on my '72 Challenger.
But seriously. I bet if you talked him down a bit you could get the '72 for 13-14k. And if more original looking is your thing, the '72 is really only a rim/tire change away from looking a lot more original.
Either of the other two cars are probably $20 to $30k and YEARS away from being on the road. The '70 appears to be the better deal of the other two, but only if the sheetmetal work has been done properly. If it wasn't, it's more work than the rusty car. That 'cuda is not for the faint of heart either. That one could go either way, it might be mostly cosmetic, or it could be a rusty disaster. Even if its mostly cosmetic there's a lot of work to do. As far as the '70 having a higher resale, maybe a little bit. It's going to be non-matching #'s no matter what, and it was only a 318 car to start with anyway. Not exactly Barrett-Jackson material. You'd probably get your money back on a resale, but its no gold-mine.
If the '72 is solid and doesn't need a full resto, it's a no brainer for me. You can drive that car right now, add a few touches here and there, and never need to sink tens of thousands into a full resto. The money is a big deal, but the time is even bigger. Full restorations take YEARS. A few if you're lucky, a lot more than a few if you're not. Meanwhile, you could be driving the '72. Sure, you won't make any money on the resale of the '72, probably none at all. On the other hand, you can drive and enjoy it. And keep in mind that if you have to sell either of the cars that need a full resto before they're fully complete, not only will you not make money, you'll probably lose a ton. Without even having any fun along the way.