N pros:
realistic scenery-train ratio
able to fit in more in less space
able to model big scenes with less compression in big spaces
ability to model longer trains, especially in the modern era
N cons:
low availability of steam models
low availability of passenger car models
low availability of caboose models
almost impossible to add onboard sound
local switching difficult due to small size
I'm not sure where to put overall detail level. On one hand, it's nice to be able to ignore a lot of fine detail for the overall look of a layout, but on the other hand, many people like a lot of details. It's a judgement call.
As to which scale you should choose, it's a tossup. In N scale, you're better off if you want to run long trains. If you want to run some trains around, but are mostly interested in local switching or steam-era modeling, HO is your best bet. And in either case. having a 12x12 room will allow you to model successgully in either scale. I know a lot of modelers who would give an arm to have that much space!
