My two cents…
Personally, I go for the fewer and quality. I am lucky enough to obtain a special relationship with sportsbook that offers my players “special bonuses”, and I exclusively promote them.
I personally feel that offering every site under the sun makes your site look like an affiliate farm. A lot of gamblers understand that gambling-related sites are affiliates. If you promote one or two trusted sites and maintain a relationship with the programs and your players, I believe it gives you more credit.
I know from my discussions on sport betting forums, that most see the “more the better” approach as site that doesn’t really care about their players and community. They view the ones that offer one or two as better sources because they believe they have a “special” relationship with them. In many cases they are correct.