A real fan favorite and prob one of the more expensive frames is the R1. It's my favorite, and to me, it's the total embodiment of what the X-Metal was meant to be. Not to take away from any of the other frames, as each is beautiful in its' own right. R1 is probably the largest X-Metal frame, so another factor to consider is the size of your noggin. If you have a large noggin, R1, XX will fit a bit better. The XS, Juliet, Half-X, I'd say fall into a medium category. And the smaller frames would be Penny and Mars. R2 I cannot speak on, as it is currently the only frame I do not own, although I will eventually.