That's a loaded question and you will get as many answers as people responding. Some will say Provari, some Zmax, ihybrid, titanide... The list goes on and on. Best course of action is to decide what features are the most important to you and then do a bit of research. What kind of thread platform do you want? Is your primary delivery system going to be cartomizers, replaceable coil
tanks or clearos? Do you drip instead?
I went whole hog into VV mods and ended up wasting a lot of money. More and more I find myself reaching for my fixed voltage mechanical
mod and controlling the vape with different resistance coil heads.
Long-windedness aside- the best mod out there is the one that meets your specific needs. Find something that seems like it will do the job and research the threads here.
Lots of great info on just about every make and model you can imagine.