I suggest to keep it for one month forwarding all the traffic to your primary domain.Then depending on the traffic sell it or keep it.
Just one curiosity, can you state that you do have the best web design studio, company? or do you offer the best services? Compared to what, who? My opinion is to pick a unique domain, not a spammy one because for sure you can do something unique when you are a webdesigner, but beeing the best .... I don't know Is just an advice.
If I were to pick out of those two I'd pick TheBestWebDesign.org as it is keyword rich. But personally I don't register .ORG domains unless I own .COM.
I don't really like either of them - I know keyword in domain is helpful but building your brand (unique name) would be better But between these two - .org doesn't really fit the www services so go with .net
bestwebdesignservices.net use this url, its best as it contains various keywords in this url, even it also learn to easy.