IMO it all depends on the type of site/s you are going to create and promote. If you had a single domain that allowed you to promote a wide range of products you could go the WP multi-site route and have for example hxxp://poker.mydomain.com, casino.mydomain.com, bingo.mydomain.com etc. This would allow you to create a strong single brand name and allow you to promote a wide range of products.
If each of your sites are going to be completely different then I would go for a separate single WP install for each. This would also make it easier to move sites around to different server locations if required.