I have thought of this as well. Rather than settle with just one set of tires, I now have 2. Summertime... 305/40R22 street tires. They're so damn expensive though that it kills me to run them through the fall rain, winter snow, and spring rain again. That's where the all terrains come in. 285/60R18. Everything mounted on their own wheels. Swapping everything out takes me all of 15 minutes.
Doing the math, both of these tires run at 31.5" tall. (Well, .1 over and .1 under). But they look totally different and serve different purposes. Don't just think about tire SIZE.

Consider tread pattern, width, and most of all, what you're going to be doing with them!
Good luck with your choice of rubbers!!! LOL