Since you are interested in battery life - 510 has bad battery life - about 2-3 hours max, less if you vape heavily. They do make longer mega batteries for 510 that give 3-5 hours (less if vaped heavily). If you want longer you have to go to Ego or Riva 510, the 6-8+ hour battery life models of 510.
KR8-based has the most prefilled cartos but it's a dedicated 2-piece unless you add parts from other models. With its standard batteries it has the same 3-5 hour battery life as 510 with mega battery.
Cartos and extra long battery life
Your basic choice again comes down to 510 vs KR808D-1
Ego or Riva 510 for 510-based
Elegant Easy (from CigEasy) or the PigCig for KR808D-1 based
Note for any of these you can get portable charging cases for charging on the go. But the 510 with standard length batteries might use up the charge in the portable charging case during a long day if you vape heavily.
510-based (especially in fat battery form) has the most options and accessories of any ecig. Few prefilled cartos but lots of blanks ones, atomizers etc. With the Ego you would also be able to use all of the low resistance harder hitting cartos and attys as well as the new tanks.
Prefilled is just a convenience for the first drags anyway - whatever you get you will be adding ejuice to. A cartomizer does not last as long as a pack of cigs despite what liar rebrander sites say. But if you add juice while it is still wet, a carto may last a week or more.
Whatever you get, get manual batteries. Less work, more consistent hits, more sealed against juice leaks (which also means you can try the dripping method with an atomizer), won't turn on by accident from wind or vibration
I use both 510 (mega manual) and KR808D-1 (standard manual). I was light smoker for the last decade of smoking. I don't need LR parts for more TH. And I am almost always near AC for charging, own PCCs for when I am not.
I bet within 2 months you will be vaping other flavors. It creeps up on you with those flavor tobaccos like 555 and RY4 and others. Real cigarettes have flavors in them - just look at the ingredients of your favorite smokes on the manufacturer's website and you will probably see cocoa, honey or sugar, and for some licorice. Many of the ejuice tobaccos have flavors in them too - honey flue cured, 555, RY4, chocolate tobaccos, vanilla ones etc. They got me eventually. I am now mostly vaping vanilla and a tobacco that has some cocoa in it (and I add more cocoa)