Yeah, it's too bad you couldn't buy them both, but I can fully understand why you can't.
Personally, I would go for the Cutlass Cruiser. I think they're a rarer car, but the downside is that parts for them might be a little harder to come by. Chevy parts are a little more plentiful, but all wagon stuff is getting harder to come by.
I personally would get the Olds and swap dual headlamp header panel for the single headlamp header .. I think they look a lot better...just my opinion.
In any case, go for the one that needs the least amount of body repair. Rust being the major factor in whatever you plunk your money down on.
If you can, could you post a pic of them both?
That '58 Brookwood is cool and getting hard to find these days. I always wanted a '58 Yeoman 2-dr wagon, but I know I'd have to pay up for one.
Good luck! Let us know what you decide. Btw, post a pic of your '59 Biscayne. A friend of mine had one back in the day. All black 2-dr post sedan...awesome ride.