I got a DNA40 and a VF ver 3 clone about a month ago and have experimented with both Ni and Ti in them. I'm preferring the Ti so far because of the easier handling. Twisted Ni and Kanthal also works.
The downside to using anything other than Ni in these mods is that your temperature calibration is going to be off, but I've found that's pretty easy to work around in practice. I've also heard of a couple of mods lately that allow you to set a resistance coefficient for the wire which should allow us to calibrate for both of these wires.