T1 faction Navy/Fleet drones have the most tank, even compared to T2 drones. The down side is that the only source of T1 faction drones (that I know of) is from faction warfare NPC corps, so they are the most expensive drones. There are also drone durability rigs that increase the tank of drones.
Having said that, my biggest gripe about drone management is that you cannot mix different types of drones into the same designated drone group. I’d really like CCP to make it possible to have drone groups that were not all the same type of drone.