What features do you wish to advance up to? More battery capacity? Better variable voltage? Variable wattage? LED display with voltage and ohm resistance meters?
The eGo Spinner 1300 mAh will give you slightly more battery capacity and better variable voltage.
The iTaste VV V3 will give you even more accurate variable voltage and wattage regulation, an LED screen, built-in ohm reader, and pass thru ability.
The iTaste MVP will give you all of the above with even more battery capacity (2600 mAh for 2 - 3 days on a charge) and pass thru ability.

