Dedicated outlets, 10ga, and what else?

I asked my electrician for 10ga romex for my dedicated outlets, and am using Albert Porter's cryo'd hubbell outlet, but the electrician said since I'm living in a commercial building, I can't have romex. He suggested THHN (but also has I think BX available).

What would you suggest I go with... the THHN or BX? (I have no idea what either is!)
i just did the same thing with 2 runs or 10 g bx cable,& 4 porter hubbell' are in for a real treat,BUT,it will take around a month to burn in(so hang in there).read the discussion on "only needs 50" & never doubt yourself,eventually you soundstage will expand beyond your wildest dreams,then the sound will tighten up,enjoy
THHN is a type of insulation temperature rated for at least 90 C. BX is a flexible outer jacketed cable with several insulated conductors inside it. My preference would actually be 10 gauge MC which is a metal clad flexible multiconductor cable which already has a full size ground wire in it. BX typically relied on the steel outer jacket with an internal flimsy aluminum drain wire to act as the ground. Thin wall conduit is also permited in commercial buildings and would be an excellent alternative as well.
I think regardless of your selection they will all deliver the same satisfying effect. Alexandierj gives some good advise that I agree with.
If you are in a commercial building, I would suggest MC or BX with isolated ground receptacles. Lots of motors in commercial buildings: air conditioners, elevators, pumps etc. which can cause emf reflections in your circuits.

"THHN" is nothing more than a name or identifier. It means the copper wire is covered by a sheathe of thermoplastic insulation which has certain resistance to temperature, chemicals, abrasion, whatever. This is the red, black, white or green color of the wire. The important thing here is that this designation is meaningless - it only refers to the jacket NOT the wire or any properties thereto. Other designations for wiring is THWN, RHW, RH, XHHW, and dozens of others. Again, not important to you - the copper underneath is all the same for a given size.

BX is a designation for a set of copper wires (covered with THHN RHW RH XHHW whatever plastic) inside of flexible aluminum armor. This whole package is referred to as a "raceway".

Don't sweat it too much. Raceways of BX, MC or Romex each has the exact same copper wires in it. The only difference is that Romex and MC doesn't pick up all the RF/EMI that BX does; but with isolated ground receptacles, BX is just as effective.
You may wish to try an all-Teflon 12AWG like the Belden 83802 also. Double shielded, too.