Hi James, there's all kinds of reasons for using all kinds of different scopes, portability for travel, weight etc.
I have both a 10" and 12" and use them both. Folks will say that view's are just a little brighter in a 12", thats the reason for getting it in the first place. Just because I thought it was worth the expense for me, don't let me talk you into spending hard earned money.
You will get something like 44% more light from the 12", that aint too bad. I noticed the very first second what 44% more light looked like, you see more, the same but brighter. Remember aperture rules even if it's just 2" bigger.
I knew that I wanted more and you make up your mind if you want more also. I'll use my 10" a couple day's then switch to the 12" and it is very noticeable as to how much more light 44% is. Thats almost half again as much light.
If you have room for both don't get rid of the 10", they all have their own uses. I think if I had to I could make room for 20 dobs of all sizes, plywood and shingles aint that high. HA! HA!
Good luck on your decision, Darrell