If you are looking at the Aspire line, I have the Triton mini, N Mini and the new Nautilus 2. The N2 has the smoothest air flow and beats the others hands down. Very tight draw if you want or you can open it up for a restricted DL sort of. The Triton mini can be Mtl it leans more toward the restricted DL side a little more. IMO. The new .7ohm Nautilus coil seems to work well in it opened up. (But then it's not really very Mtl) The T mini seams to be midway between MTL tank and a Sub-ohm tank.
If you want to rebuild a Kayfun 5 with the reducer kit can give you a good MTL experience and has the ability to open it up without the reducers and get a lot of airflow...
There should be a new Kayfun coming out soon. You might want to wait on the KF5 to see which one suites your style before dropping $120.