Truer words.....I almost never fly outside of Orbx regions anymore.
I'm somewhat biased towards PNW as I live in that region.
If you are set on just one region then Australia gives you a lot of choices and the most freeware airports. I got that region last Christmas and am still only scratching the surface.
You might consider PNW and NCA. Seattle to San Francisco. Vancouver B.C. to Sacramento, Portland to Redding.
Really though, If the area you live in is covered by a region or are personally familiar with the area covered by a region I'd start there. It is rather fun to fly in areas that you are already familiar with and have or potentially could actually visit. I live several miles from a modeled airport and visited once out of curiosity and it was interesting to walk around a place that I already felt like I knew
That being said I'm debating myself, Norway and eventually the rest of the Europe regions, or finish off Oceania with NZ:North Island. Whilst debating over A2A planes that are also on sale.
Orbx typically has a sale twice a year, so once May is up don't expect another sale until December. If you buy now and love it you can add another region or two before the end of the month which will likely give you plenty to explore until December.