Screw that, get a Octo-26650 Box Mod and a MutationX v4 and rock that. - Just kidding -
Depends on what you want. Longevity - the iStick 30W is a good suggestion or a Vaporshark rDNA40 with a good nickel build inside a tank would suffice. You can not only lock your settings on both, but they're pretty small and offer good longevity for what they use for batteries. As far as I know, the iStick 30W uses a build in battery whereas the Vaporshark uses a single 18650 that can be charged and vaped on the go - which offers flexibility as well. If boxes aren't something you want to tote with you - look for a regulated tube. The Eye, Semovar, Provari (just to name a few) are pretty good, set it and forget it, although they're pretty bulky in some people's opinion - but they just work. Battery life on them varies based on set voltage / wattage - the higher the power output the shorter the life. That applies all across the board. I would suggest ego style pens - but based on my opinion and experience - they're more problematic than they are a solution. As the tanks are (for the most part) pains in the ... to maintain, small capacity liquid levels, have a tendency to fail (either through shoddy made coils or how the coil heads are manufactured with holes in the contact pins that allow juice to drain onto the contact area of the battery), and offer lower battery life. So depending on how long you plan on being in the car - from point to destination - will determine what you're looking for.
Oh and if your car has a certain color combination - get a Provari to match it.