Many many variables... but when I actually monitor my usage, I find I tend to go through somewhere between 4 & 5mL of fluid when using Clearos, but it seems to have settled down to somewhere around 3mL (possibly less) with EMDCC's. The Clearos seemed to give a "wetter" hit, possibly using more fluid per hit? Whereas the EMDCC's seemed a little dryer but also a little more satisfying, so I think I'm vaping less often and for shorter periods with them. However, I vape substantially more if I'm bored and/or sitting around doing nothing of course, lol...
EDIT: reading the post above, I realize Clearos probably use LESS fluid per hit (depending on voltage, ohms, fluid, etc), but I do think less is absorbed with a "wetter" vape, so I was probably hitting them more than I was with the EMDCC's.