Indoor is always " artificial " whatever the surface. Full carpet is interesting but as has been said, is touring cars with jumps..!
Outdoors is where it's at....surface, whether astro, mixed, dirt or good old fashioned grass, is very much down to personal preference. Astro is good, easy to maintain once built and cars stay clean.! Personally, I think that a good, well maintained, grass track is great but, probably, not many will agree with me..!