Types of robots:
Maximize the types.
brainbots: small, cheap, weak, not much carry, nice for beginers. Can carry and dig. Can only run away (and will).
Mr handy: a little more capable, more expensive/difficult. Can carry more. Can only fight by melee.
T-51d: uses pa skins. Can dig as well as anything else. Can also fight (but only whoever's attacking it/you) using melee/pistols.
PA2: uses apa. Can do anything a T-51 can do, but is tougher. Can be used as a merc.
PA-3: frank Horigan skin. Much tougher still. No heavy weaps except laser rifle.
Warbot: the enclave combat robit. Very hard but can only kill kill kill, can only use heavy weaps.
turret: supremely hardened, self-repairing, can't move so can't dodge (really hard to miss, like automatic 99% hit). If you wanna take one on, better bring a team. With BIIIIG guns. And really good armor.
Each would have higher craft requirements; some junk and a few sec's might get you a brainbot, but for a turret your talking adv. alloys, gmp's, refined uranium, it's gonna cost you.