I am finishing a new bonusroom/playroom upstairs and would like to know the best brand/unit for the job? Looking at approx 500 sq ft.

Why a portable? Can't use a window combo unit? With a portable you need to empty the drain container or run a hole in the wall and most portables are not heat pumps, they are resistance units. For that size room, should run about 8,000-10,000 BTU for AC and 10-15,000 BTU for heat. A lot depends on where you are located, shade, insulation etc. You could also consider a mini split ductless.