I use reggies with great results ...... !!!!
I agree that if budget were not a constraint then aragonite would be best, however this is not for the "traditional" reasons. I am a geologist and this "buffering effect" that is proposed as one of the best resasons is in my educated opinion, not effective in a timescale required for an average fish tank. Geological processes happen over millions of years...... whithout launching into a scientific dissertation, there is no way in my opinion that the requirements of a fishtank from a chemical perspective can be met by a geological process, at least not close to the level of efficasy that we demand in this hobby. I would choose aragonite for 2 reasons alone, first the Specific gravity of Aragonite is 2.9 versus reggies (which is essentially quartz) which has a SG of 2.65 .... essentially the aragonite is heavier per given volume than reggiess (in general aragonite has a larger particulate size which magnifies the effect)..... what is the positive of this ... simple, the particles are less likely to "blow" around in the current. Secondly the aragonite particles are generlly rounder which as crispin pointed out is important for the little bugs living in the sand. I am told that aragonite holds its whiteness better than reggies, but have no comment on the validity of this.
Pool sand... no ..... in my opinion the particles are extremely roungh in comparison to the other options and not worth persuing. I would also worry about the chemicals as per crispins comments.
Reggies or aragonite or local sea sand ...... all effective if used in a PROPPERLY designed and thoughtout filtration system..... the sand is simply one component of the system.