As someone who owns both and have tested both, you are better off with the FlyTampa version. RegDesigns is beautiful, its a stunning airport inside and out. The price for that is FPS. It is a resource hog.
They have stated they will work on optomizing it, and have released a texture pack (which reduces the textures by 50%). it is not pretty in the least, but I guess will get people by for now who want to use it.
I did some comparisons and posted here;
In short, unless you have a high end GPU, I would stay away from RegDesigns for now.