MVP2 is hard to beat for the $40 you'd pay for one. A lot of members have them and assuming you are OK with the form factor, they are an excellent choice for both new and not-so-new vapers.
I started with a genuine Vision Spinner - I still have them. They are excellent batteries with good quality threading, great run time, variable voltage and all in a slim package that is easy to slip into a pocket. Together with the Twist, they are something I would have no hesitation in recommending. They run around $20 each.
Finally, every vaper should have at least one back up battery, charger and topper so I'd also recommend getting more than one.