Hummingbird Feeders
Here are a few things that you should look for in a hummingbird feeder:
Color - Hummingbirds are attracted to the color red. That should not be interpreted to mean that you should only have red feeders, in fact just a splash of red can be just as effective, but some red somewhere on the feeder can help attract hummingbirds.
Pest protection - With it's sweet hummingbird nectar, a hummingbird feeder becomes quite attractive to some pest, specifically ants and bees. Ant moats may be built into the feeders or you may be able to add one to solve the ant problems you see. Another solution is to cover the hanger with a barrier like the sticky guard made to apply to trees, or even something as simple as Vaseline (this will need to be checked more often to keep it fresh.)
Bees and wasps are attracted to yellow, so try to avoid yellow parts in your feeder. The shape of the feeder can also reduce the likelihood of attracting bees, check the product info to see if that is a feature.
Perches - These birds like to rest and feed, so accommodate them with a perch.
Feeder size - A smaller feeder is often adequate, and it's usually better to have multiple feeders if you have a lot of birds. You don't end up with a single dominant bird that way.
Cleaning - These feeders should be cleaned often, in warm weather up to 2 times a week. With that in mind, look for a feeder that that is easy to clean, with no little hiding spots to develop mold, and the assembly is easy enough to allow you to reassemble it without spilling the nectar.
Mounting - Out of the sun is better, as it will reduce the tendency to grow mold. You may also want to consider the local wind conditions, even to the point of choosing a feeder that has reduced wind resistance.