I know that the best way to determine frame size is to ride the bikes you're considering buying. But when you can't ride them, and just have to choose based on your experience, that's where I am, and I suspect many of us are.
I have a 19'' hardtail and a 19'' ds and have demoed 14'' thru 18'' hardtails and find them all to be okay. (I'm 5'10.5'' tall with a 31'' inseam.) The 19'' mtbs are a bit big for me, and I notice little difference with the 17'' and 18'' mtbs. So I'm focusing on a 15'' or 16'', basically a small size, depending on how the particular manufacturer sizes them. A 17'' or 18'' (medium size) is what convential views indicate I should ride. But I feel that a small size will allow me to throw it around easier by being able to position farther fore and aft.
My survey questions are:
1. Who went with a smaller size mtb (for your height) and are you satisfied with your mtb? Why?
2. Who went with a regular size mtb (for your height) and are you satisfied with your mtb? Why?
3. Who went with a larger size mtb (for your height) and are you satisfied with your mtb? Why?
Any other thoughts on frame size are appreciated also. Thanks.