By no means do I want to hijack your thread, but I've had the similar question. I'm personally not looking to make huge profits and get rich quick but mining as a hobby and hitting ROI would be nice.

I've seen some speak about increase in difficulty in some common alt coins that could phase out AMD cards. I'm still doing a lot of research if it will be all AMD cards or just the lower end cards with low memory (i.e. 3 gig cards). This same logic could be true about NVIDIA cards as well that have 3 gigs.

I'm interested in seeing others responses but wanted to throw in another way to look at the AMD versus NVIDIA angle.