Depends on the local code requirements that your HOA is following. In some states, though not common, hollow (metal/Alum) conduit is required to be bent and set, then solid wire fished through. MC flex cables may only be used for certain lengths of runs. It all depends... If you don't know your local code requirements, as said before, consult your electrician first before picking products. A licensed electrician will know the code.
What wire to use instead of Romex
I want to install a dedicated 20amp outlet (likely an AQ NRG). The run from the main panel in the garage to my living room above is relatively short - maybe 25 or 30 feet. Because of HOA rules/regs, I cannot use Romex. Wires in the garage must be inside conduit. I will run 10AWG, but I'm unsure what other specs I should implement. Should I use solid core or stranded? Should it be copper? Is BX the way to go? I've read where using stranded silver or silver tungsten is best, but I'd be concerned about the silver oxidizing/tarnishing over time, especially at the junction points where the wire has no insulation. Is it important to twist the three (including ground) wires or will they perform just as well if run side-by-side?