Also worth considering that many seahorses aren't tank bred... and in this day and age that's a tragedy. I live in DC and I was at the Baltimore Aquarium, where they have a whole exhibit on how the pet trade has almost single handedly wraught havoc on the seahorse population.
Tank bred horses, which are springing up more and more, are heartier, last longer, eat less selectively, and aren't contributing to the decline of the hippocampus population. Just be sure yours are tank bred before you go that route.
That said, sea horses and pipe fish rule, and should they fit the criteria, I think they make their owners very happy every single time.