I would have said the Vamo a week ago, but since I received my iTaste SVD, I'm really digging it. Affordable, under $100, telescoping so it can take 1x 18650, 1x 18500, 1x 18350, or 2x 18350's. Variable voltage, variable wattage, ohm checker, battery life indicator, menu is easy to learn, and the buttons LOCK! Yes, they LOCK! Woo hoo!! That was the biggest turn off for me with the Vamo. No locking buttons.
I would also suggest an iTaste MVP, but I've been encountering more and more people having troubles with their MVPs. Plus, the MPV IS the battery, so once it's dead, it's dead. No replacing internal batteries.
If you do choose a tube mod, or even a mech mod, you're going to need batteries and a battery charger, also.