PVE or PVP focused?
For PVE you want something that can heal, so a mage.
For PVP healing is not that important because players will usually out dps your heals. I enjoy combining a pet with a high dps meele fighter...
Currently I can think of 3 mainstream builds:
1) Human mounted mage with horse + pet
2) Human mounted archer & mage with horse + pet
3) Human or sheevra foot mage with pet
2) is mainly for ganking.
1 & 3 should be able to solo certain PVE mobs e. g. trolls with a turtle as pet.
Humon is mentioned so often because they got lots of attribute points (and therefore more skill point Bonus from attributes) and skill point bonus for mounted skills. The total amount of required skill points will be your main concern as tamer/beast master.