An SVD, MVP, or a Vamo would be my suggestion. I'm partial to the SVD, but that's just me being biased. If you're going for a tube mod, you're going to need external batteries (the SVD can take 18350, 18500, or 18650 batteries, the Vamo either 19350's or 18650's), and a battery charger. Unless the vendor supplies them in a kit. However, I wouldn't trust ANY battery charger that is included in a kit. Best to toss the included charger completely and buy a Trustfire or Nitecore charger.
+1 on these recommendations. Any of the above will do. I went with the Vamo V3 for its eGo compatibility, power management features and sleek design. I also bought 18650 and 18350 batteries and already had the charger. Once I paired it with a ProTank 2, I was satisfied that I'd taken the right path.
The SVD and MVP are solid choices, too. Take your time. Read the forum and mull the features of the devices compared to what you're looking for. It took me weeks to make up my mind. Again, it's hard to go wrong with any of them.