Re Vapor4Life - if you don't run the cartos dry and singe them, you can get at least several days use out of each. Choose manual batteries. If a carto leaks it will leak right at the spot where an auto battery can be more easily damaged or killed. Auto batteries can also turn on accidentally from wind or vibration. The standard Vapor4Life batteries are 280mah so about 60% more charge than standard 510. And if you want to start with prefilled then a Vapor4Life/KR808D-1 is your best choice.
Lights smoker - I would say try their 18mg and their 11mg, The 18mg can have a lot of TH (throat hit) on that model because it and similar 2-pieces do run a bit hotter than other minis. Their Cowboy or WOW Cowboy is their Marlboro-alike. I like thei WOWboy (a deep cocoa tobacco flavor, and WOWBoy is the same with some mint added - both can be tried in the WOW Tobacco sampler plack of cartos). I like their WOW Vanilla too and those are a good flavor or topping off with any fruit flavor juice.
If you buy blank cartos and fill them (18+ drops) with fairly thin eliquid (V4L non-VG liquids or other liquids with 30% or less VG in the base) and clean up the carto, I find laying it on different sides for 15-20 minutes is enough to get all fo the stuffing damp. If you use thicker juice then you may need to let a freshly filled carto settle a lot longer. but no waiting is needed when you just add juice. When I am vaping, if the vapor seems a bit light or a bit dry or the carto is getting warmer than normal, I take it off the battery, open it, add a bit of juice, clean up, and continue to vape. I often use a plastic or delrin drip tip as a mouthpiece on the carto - nice size for the lips and easy to pull out to add liquid.
Whatever you get, you will be adding liquid. It just isn't very economical if you use a carto once and throw it away. Why use up 1-2 cartos per day when you can get 4 days or more use out of each. Of course if you are rich then you certainly can buy lots of cartos and do exactly that. I find some of the Vapor4Life flavors too strong and harsh. 11mg is less harsh than 18mg. And you can top the cartos off with juices from elsewhere that have smoother hits (like juices with 20-30% VG in them).
You can also try cartos from Bloogplanet, Smoketip, VapeSafe but I don't know if any of those are as easy to refill. Some may need messier tricks like pushing the juice in with a "carto condom" (the little silicone caps that come on the ends of most cartos).
The other best choice for a slim ecig is the Joye 510 manual (Cignot.com and elsewhere). The standard size is only 180mah but if you keep the other battery charged then that is not a problem. I have chargers at work. I have the nice PCC charging case from NoSMokeVA.com for charging on the go. I use blank Boge 510 (standard resistance) cartomizers which are very nice cartos and usually give me a week or more of reuse. There is also a 1-inch longer 510, the Joye Mega XL (128mm long with a cartomizer, and 60% more battery charge, same charge as standard Vapor4Life). These are very nice, the only downside being the PCC for these is metal and not roomy at all. Another downside for you might be that there are very very few prefilled cartos for 510. Nice thing about Joye 510 manual is they are totally sealed on the threaded end so very safe with refilling cartos, very safe for dripping on an atomizer to test juices. Another nice thing is 510 is the biggest family of stuff - upgrade paths, styles of cartomizers, even little tanks some people like (but they don't hold as much as a cartomizer). Re upgrades path - I actually carry a charged Riva 510 battery with me. If I ever screw up charging the slim ecigs or are stuck away from power for many hours, I can vape my cartos on the 750mah Riva 510 battery (and I do sometimes just because it give a bit bigger warmer hit).
If you want a slim ecig, one of those two are most recommended.