in general if the 2name is very good and looks good, then take the hyphen .com, but not before checking out possible 3name .com. Use .net if absolutely premium name or is net-connected, otherwise don't bother .net is over-rated as a generic extension IMHO.
the only time i would register a hypenated .com is if if the un-hypenated url was a parking page, otherwise you will potentially lose a lot of traffic to a competitor.
it's easier to brand a non-hyphenated .net domain name as compared to a hyphenated .com (unless the individual keywords are very strong). So, if you're thinking about branding, the .net version is better. Generally, it's better to register both, if you plan on launching a site on that name... if you change your mind after some time, you'll have options... so reg both.
My personal preference would be a .net over a hypenated domain name. Consider a scenario when someone verbally say "sport-forum.com" and "sportforum.net", the .net seems more long-lasting in the mind than the one with - in it.