In addition to the two ferries that ply the waters between Anambas and Pulau Bintan, there's the Bukit Raya. This passenger cruise ship is capable of carrying close over 1000 passengers between Bintan and Anambas.
Bukit Raya offers KTV, provisions shops, a movie theatre and other kinds of entertainment. Tickets come in regular tickets for seats, as well as full-on sleeper cabins, which allow for a guaranteed good night's sleep along the way.
Speaking of sleep, keep in mind that the Bukit Raya isn't nearly as fast as the fast ferries, which means that it can take up to 20 hours to reach your destination. The other thing to note is that the Bukit Raya only services this route twice a month. So if you're not planning to stay in Anambas that long, then it's probably best to book the fast ferry there and back.
Alternatively, you can take the Bukit Raya for your outbound leg and the fast ferry for your return. Or, if you're in a hurry to get to paradise, go to Anambas by plane.
Lastly, please note that Bukit Raya doesn't really go per any given schedule as such. By and large, it will ply its route every two weeks or so, but exact travel dates depend on demand. In other words, only those who have a lot of flexibility in their itinerary are advised to take the Bukit Raya as their mode of transport to Anambas.