Most people start with one of these
Manual batteries recommended for all. PCC charging cases available for all.
Joye 510 - slim, small, starts as a 3-piece but can be used as a 2-piece. Very supported - lots of atomizers and cartomizers available for 510 models. Low battery life (1.5-3 hours or you can get the inch longer mega xl batteries for 3-5 hours charge life, all charge lifes less if vaped constantly) - I use blank cartomizers on one of these - been refilling the same cartomizer for over a week. Fewer prefilled cartos available, lots of blank types
KR808D-1 (also sold in colors at Vapor4Life.com) - a dedicated 2-piece with plenty of prefilled cartomizers available and a smaller selection of blank cartomizer. Battery life as long as 510 mega batteries (3-5 hours). Thicker than a 510. Probably the 2nd most retail market-supported model after 510 models.
Ego, Riva 510 - fat battery version of 510, battery lasts 6-8+ hours, can use more power-hungry harder hitting LR (low resistance) 510 atomizers or cartomizers. Anyone who needs or wants this extra longer battery life or harder hotter drags or the ability to use tanks of juice is advised to go right to these models.
BTW - prefilled cartomizers are just a slight convenience because whether you use carts or cartomizers you will be adding ejuice to them. Carts and cartos do not last as long as a pack of cigs. That is a web rebrander lie. But if you add juice while they are still damp, they can last days to a week and sometimes more.
Yes - I spent a lot to get started. I spent more to set up charging and cables at home and at work, get a PCC, get spare parts - but at least I paid normal retail prices, not jacked up "made-up name" model prices. I spent a good amount finding 2-3 all-day juices I like. But now I mostly just restock my favorite juices and several I like to use for variety. And I buy blank cartos and usually get 4-7 days out of each. So yes - I invested in my health.