One of the most raved about are diatomic filters, like the Vortex or System I. But these filters are a major PITA. Becuase you have to prime them each time with then add the container with the diatomic powder. If powder gets on the rim of the jar, then you could damage it. Plus, diatomic filters cannot be run 24/7, since they will burn out.
Magnum filters are second best, because they use micron filters and you have the option to add diatomic powder to it.
The diatomic filters are hang on filters, as well as the Magnum 250. The higher Magnum filters are regular canister filters. The Magnums can be run 24/7 in conjuction of a regular filter, but keep in mind Magnum filters do not have great biological filtration.