14 to 15 inch spare combo

The rears are really the only ones that need to be the same size, and only if you've got a sure grip.

If you go with significantly different sizes on the rear axle you'll wear out the clutches and overheat the rear end in fairly short order. Probably not a huge deal if you're just trying to go a few miles to get off the freeway to a tire shop, but much more than that wouldn't be a good idea.

For a single legger it doesn't really matter as much. Same for the front, only real limitation is the tire height fitting into the fender. Like if you're running 28" tall rear tires and want a 28" tall spare to work with your sure grip rear end. Kind of moot in that case though, because the tallest tire that will fit in the well is 26". It'd be nice for the spare to be close to the same size if you don't want the car to sit all wonky, but again for short distances the change in alignment on the front isn't a deal breaker. The spare I posted above is 26.1" tall, which works for me because my rear tires are 26.1" and the fronts are 25.6". Close enough for the rear with a limited slip, and not a deal breaker for the front either because its so much narrower than my 275/35/18's that it clears fine despite being taller.