Why SSD over HDD (I mean it isn't really such a problem while playing - only when you install/copy/uninstall/cut/paste/delete something - while SSDs are a lot more expenisve than HDDs)?
On topic: Desktop definitely - I have an AMD Phenom x6 1090T, 8GB Ram, 1TB HDD 6Gb/s, ATI HD6790 1GB DDR5 - everything runs perfectly on it (considering the fact that I got it for around 700$ I think it's great) - while if I buy a laptop for gaming - 1)it will be really expensive if I want to be able to have an enjoyable playing experience, 2) it won't be worth it because in 1 year it will be already considered extremely old (if it hasn't melted already).