Some people are resistant to trying a fat model first. If you decide to get a slim model then for something decent and fairly foolproof I recommend Smokeless Image Volt manuals (or Bloog manuals is the same model) - manual because easier to get a good drag, harder to kill with juice leaks. Almost every more powerful model and mod is manual because it works better and is harder to damage, as well as generally safer (wind and vibration can't turn on manuals). I like Smokeless Image's Volt and Bloog manual batteries that are around 300mAh though as a newb I briefly preferred the shorter batteries (decided the charge of the short ones doesn't last long enough). Between Bloog and Smokeless Image there are a number of sample packs of cartomizers (can also use the standard V4L.com cartomizers andf their sample packs of cartos for trying flavors). The cartomizers can be kept damp with eliquid to get a week or more use out of each. If a cartomizer is allowed to get too low on liquid, it will singe and taste bad, like lighting a cigarette filter.
Tip: a simple flavor eliquid like Vanilla can be used to top off fruit and dessert flavor cartomizers, and a plain tobacco eliquid can be used to top off any tobacco flavor (as well as fruit flavors and dessert flavors for a flavored tobacco mix).
These are regulated 3.6v batteries w/ KR808D-1 threading. Nice and strong for a slim model and available in lots of colors. I am not a pink person but I do like the darker pink Raspberry-like colors of these batteries. I use a drip tip as a mouthpiece in place of the cartomizer endcap - that way I can easily pull it out to see if the top of the cartomizer's stuffing looks dry, can add liquid (with carto off the battery) etc.
Issues: You sort of need to know if each of them smokes regular or menthol cigarettes and the strength of the cigarettes they smoke (full strength, lights, ultra-lights each have different amounts of nicotine and therefore throat hit)