time is the more important consideration... i don't have a domain that doesn't earn back reg fees. but that's not a great return, but at the same time it's not losing money. so start building some sites, earning some money, and then take it from there. split test - try one as a general site and another that is a more targeted niche site.
i tend to believe that a more targeted niche site is going to perform better with search results - but there are others much more knowledgeable than me in that regard to answer.