The S-K DIREKTIONSSEKRETAR is without doubt the best anthrodrone in regard to performance, stealth and autonomous operation.
If you are on a budget and don't mind being a creepy mf you can buy the Horizon Little Buddy in bulk, give every puppet armored clothing for kids and put a gun in their hands. Add swarm soft on a RCC and you can kill your enemies with an army of toddlers.
A good compromise on price and durability is the Sparring Drone from Hard targets. It's cheap, durable and can be easily upgraded.
If you want a melee drone take a look at the KENCHIKU-KIKAI. 8 STR + a Combat Axe make them prime contenders to jump into.
It's also strong enough to carry a shield, so you can create moving cover.
For armor go as high as possible: Full Body Armor + Gel Packs are wonderful since your opponent needs to get to 21 dmg+AP to even have a chance to damage the drone (except for electro attacks, so don't skimp on the non-conductivity)
Otherwise the Big Game Hunter with Gel Packs and helmet will do nearly as well.
The nice thing is: If your drone is destroyed regardless, you can just salvage armor and weapon for the next one.