Any recommendations on what 12awg electrical cable to use? Something durable and flexible is preferable.
Don't use Romex®.
Do you work out doors? Are you likely to see a fire or electrical inspector? If so you should be Code-compliant, and Code requires "extra-hard service rated" portable cords. Cords are rated and labeled according to construction, materials, insulation thickness, resistance to ozone, oil, water, UV (sun), etc and that is what determines the alphabet soup of cable designations: S, SO, SC, W, SOW, SEOW.... If it has a "J" in it, like SJOW, the J stands for "junior hard service" and is not compliant for outdoor use.
We've been using Southwire's SEOOW 12/3, 10/4 and 10/5 cable. The "E" is an elasto-polymer jacket that is lighter weight than others but has the same abrasion resistance and insulation qualities. It handles well, too.
Also you will find that some manufacturers make the same product designation in 2 forms: a UL-listed and labeled product, and an otherwise identical-appearing product that is not listed or labeled. In some jurisdictions, in some venues, and with some clients UL listing is required of all electrical stuff; other places you could use white vinyl lamp cord and nobody official would care. We buy UL listed cables.
The big manufacturers are General Cable (GEPCO), Coleman, Southwire and Carol, but they are not the only ones. I'd avoid buying AC cable on eBay unless you know the seller and they pay return freight... there have been posts about sellers advertising #12 AWG wire that has the correct O.D., but the conductor is actually #16 AWG. Insulation is cheaper than copper...