Invertebrate Keepers and Aquarists (excluding Marine Mammal Keepers) are the keepers I've worked with the least. They are often in the odd position of working with animals of which nothing is known, sometimes not even what species it is! As a result, their professional field is one where the most changes are being made, with many new horizons to explore opening up all the time. Both are also often in the position of taking care of a group of animals - a colony, a tank - rather than managing animals as individuals.
"And that one is Skipper, and that one is George, and that one over there is Russell - oh, he is such a rascal - and that one is..."
Amphibian Keepers are often lumped with reptile keepers, which can be stressful for them. They tend to be more serious, less extroverted, and all in all calmer and more disciplined. Caring for animals which are much more sensitive to the minutiae of temperature, humidity, and water quality, they are more cautious by nature, compared to the rough-and-tumble world of reptile keepers... they are certainly more hands-off with their animals. Like reptile keepers, amphibian keepers are generally very academic and more involved with conservation than other keepers.
Bird Keepers are what I sometimes think of as the cross-road keepers. Like reptile and amphibian keepers, they take care of a wide variety of species and large number of individuals. That requires them to know a lot about a wide array of species and be able to keep track of their needs. Like mammal keepers, however, they are often expected to incorporate more training and enrichment with their charges, especially the larger, more charismatic ones, such as ratites, parrots, and raptors. Bird keepers have a weird deal, where lots of people (including other keepers) don't take them too seriously and dismiss their animals as "just birds", but at the same time are terrified of birds (big cat keepers talk tough, but they turn to jelly in the presence of an angry male crane... after all, they don't go in with their cats). Bird keepers often have involvement in conservation and a close collaboration with the private sector. If they have one major pet peeve, it's that they cannot understand why no one thinks their animals are cool.
Except for penguins. Everyone loves penguins.
Mammal Keepers are their own diverse bag of issues... more on them later.