Sand for me. I was very skeptical about it at first, mostly cuz I figured it would be a nightmare to clean/keep clean. The 75 gal tank I bought came with a sand/gravel mix, and I sat there for 4 hours with a pasta strainer getting rid of all the gravel and keeping the sand.
I think its easier in some ways to keep clean, all the polys poo just sits on top, and I use my Python about a 1/4 to 1/2 inch above it, and it pulls it right out. Then, I turn the suction off and stir up all the sand, and start pulling out more water. *I have black sand, so the poo doesn't show at all*
I haven't had issues with sand destroying the filter. I got a Rena XP3 from the person I bought my tank from, and cleaned it out, and yeah, there was sand in the filter, however, so far there hasn't been any issues with that. I just clean the filter once a month to remove the sand LOL