nzmolina,
I recently switched from gravel to sand and wont go back. It is remarkably cleaner in the tank as the debris floats on top of the sand till the filter can pick it up or I vacuum. As for cleaning the sand - as i learned from many on this site you just hover the vac over the surface and that does the trick. As for the sand itself there are lots of options - I personally used quickcrete brand all purpose sand as it is heavier and darker than play sand. After rinsing the sand REALLY well I actually was able to swap substrates with all inhabitants in the tank. Hope that helps
~Shawn