If possible try having your main keyword in the domain if its not too big to insert but at the same time its not that imperative to have it in the domain. Just see that the domain name you select is easy to remember, recall and type on the the keyboard. Small and catchy domains are the one's I would probably go for.
It is good to have the keyword in the domain and have the domain name relate to what the site is. If you tend to pick a name that is likely to be typed in, you can get some traffic for that as well.