This is something I can actually talk semi-intelligently about. LOL For 'naming things' is my #1 skill (or so I believe) and the success of websites with names like ErosExotica, Touch The Body, Fellucia Blow, MILF Mia and The Art of Handjobs (all of which I created) kinda proves this. Type-ins to those domains exceeds any other traffic I receive for those sites.
So having said all that (boasted all that, apologies) my only question is this: what kind of traffic are you looking for? Since this is an Adult Forum I am assuming your domain choices would be in Adult (tho you mentioned mainstream). I ask this question because it is the #1 factor for naming things - where ya gonna promote it?
If we talking Google/SEO alone then go with the three words that describe the site. BUT you will face stiff competition and have to fight for page rank with other un-imaginative twats (sorry, no offense) who take the 'easy' way of doing things and simply fill their domains with keywords.
IMHO the better option is a two word (or better, a single word) domain that is highly, highly unique. Even a 'made up' name will do (if it's clever). Why? Because people will remember the uniqueness of the domain and...type it in!
So to use your laptop example: I personally would never name a domain with either of your choices. Instead I would go with something like
www.dynolaptops.com or
www.lapworld.com or
www.geekslovetops.com (just off the top of me head). Something memorable, unusual, unique and sticks in the mind. Long-term you will be MUCH better off. This is the essence of branding. I mean, Twitter could have called itself
www.textmessagesonline.com or something like that but didn't.
Good luck!!