I would not recommend getting something without nicotine if you are trying to quit smoking though. For one thing, nicotine is about as bad as caffeine for you, for another thing it's not cancer causing, also it's not nearly as addictive as you might think; it's only very addictive when you get it from tobacco products. Nicotine will help you succeed with making the switch to
vaping - so don't discount it's importance in making this endeavor work.
As for which one to get, there are a few concerns to think about:
• how much fussing around are you willing to do?
If you want the easiest system then you might like the KR808D-1 (aka vaporking at vapor4life). It's a two-piece e-cig (battery and cartomizer), so just screw the two parts together and you are
vaping. With a bit more fussing around you can use the standard 510 system, it's a three piece system (battery, atomizer, cartridge) but you can opt to buy cartomizers for it if you want, just not in as many flavors as you find with the other system -- plus the battery doesn't last as long.
• how much do you have to spend?
The KR808D-1 system tends to be more expensive and the cartomizers are disposable (though they can be refilled a few times before tossing them) so will end up costing more in the long run. The 510 systems are dependent on e-juice but the basic components of the system last for quite a while without needing to be replaced so end up costing less in the long run.
• something you should know about the batteries on these things:
the more "cigarette-looking" the e-cig, the worse the battery life is going to be. If you want it to be exactly the size of a cig, you can find that but the battery lasts about 1/2 an hour. 510 is smaller than kr808d-1 but also doesn't last as long. 510 also comes in a bigger battery version called eGo (or Riva, same diff) that is as fat as a sharpie pen but the battery lasts about 7-8 hours. If you get the standard 510 or KR808D-1 you may want to also get a charging case for it so you can charge up your batteries when you go out.
All batteries have what's called a "mah" rating, the more "mah" the longer the battery lasts between charges. Each 100mah is good for about an hour of use. The standard 510 is 180mah, the KR808D-1 is 280mah, the eGo is 650mah (Riva is 750mah). ...and the cheap-o cig look-a-likes (no brand mentioned in this post, but they make them) are about 100mah or less.