Coral grow out
Something with heads are always the easiest IMO. Zoas, acans, etc. chalices can be measured with eyes. Things like acropora or montis can be difficult to measure growth as encrusting vs vertical growth is almost impossible to account for.....
So I vote for zoas or acans personally. I would pay up to at least 20 bucks for a nice piece that wasn't already all over the club, and isnt found in every tank in California.