I bought my MTB first based on information I had found online, a 24". It fits and is comfortable but too big to be really nimble and flick around on tight or technical sections like switchbacks. My next bike was a road bike, size 60CM compact. The frame feels very small but still roomy, with the top tube down close to my knees but still long enough in the top tube.

So, I feel that I sort of ended up with it backwards. I just finished my new bike last weekend and as of today had logged 105 miles on it. It closer matches the size of my 24" MTB and is very comfortable. I'm undecided on my next bike, it's between a vintage steel or a better MTB. If I do a MTB I will be looking for a frame that feels more like my first road bike.