I think it depends what your domains are..If they are all for different niche's then obviously the best bet would be to develop each of them around their niche.
If they are all related to the same niche then...do they get type-in traffic? are you trying to rank these in search engines? Will be you be advertising them via PPC or ads somewhere?
type-in traffic = redirect to your main site (use a 301 or 302 redirect)
search engines = develop..neither will get you ranked
PPC = use a nice splash page or intro page
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