I use 16x16" and 18x16" floor toms at the moment. But on my next kit, I plan on going 15x13" and 18x15" which should give a really nice pitch spread between the drums, especially when put with the 10" and 12" rack toms. I went off 14" floor toms a few years ago - I started to find them lacking in depth and generally pretty unsatisfying in tone (apart from when put into higher jazz tunings). Seems the drum industry agrees with me right now as 10, 12, 16" kits are everywhere these days. I like that setup but I think 10, 12, 15, 18" is the ultimate in versatility and tonal satisfaction.