I've done arial, human, and duergar. Arial was the best for me at all levels. The INT was a huge boost too as poisoner skills can be tough to improve and it is so expensive.

I would suggest poisoner and knife first. At 42 focus on thug up to parting block. You won't need cheap shot due to parting block and neuro. Then maybe round out poisoner up to grenade or just mind control + plant if you want (would need DV for extra thief points).

I would not do svirf, just me. shrug