Hi - some general advice
1. There are lots of bs "name" brands on the web, with glitzy sites peppered with lies and false claims about their ecig being rated the best, or carts lasting for 1-1.5 packs each or battery lasting all day. There is no slim battery that lasts all day. None of those slim ecig "name" brands invented their ecig. They just slap their name of some Chinese model, good or bad, compatible or not, and often jack up the prices. So it really is best to buy either from multibrand trusted vendors like (for example) Liberty-Flights.com or Cignot.com and know what model you are buying or from a name vendor only if you know and want the model number of what they are selling. One popular name brand many do buy from is Vapor4Life and that is KR808D-1, a full-featured KR808D-1 vendor including manual batteries, blank cartomizers, juices.
2. Super minis suck. A super-mini i.e. an ecig the same length and diameter as a real cigarette, will satisfy most buyers for no more than 30 days and sometimes for less than 1 day and then they will buy something better. For slim cigs you need at least a mini which is a bit fatter than a cig (about 9.2mm) and 110-130mm long.
3. Manual batteries are a smart choice. Most people here use and recommend manual batteries. The two most popular ways to vape - dripping and cartomizers - can both occasionally leak a bit of juice on the end of the battery. Auto batteries are totally dependent on a little drag sensor right inside a hole in the end of the battery making autos much more easily damaged or killed. Autos can also turn on accidentally from wind or vibration. Manuals give more control of your hit and are less work.
4. Buying an ecig with a popular threading means having more choices of what you can attach to the ecigarette. More cartomizer and atomizer choices, and for 510 also tank atomizer and tanks. The most popular threading is 510. Then second most popular (and the most popular for a 2-piece) is KR808D-1. And notw - if you buy a 510 I recommend Joye brand because at least one clone brand is reverse polarity and has chargers that will melt or explode real 510 batteries.
5. If you are looking for super-long battery life, or the hottest hits, then you need to skip slim ecigs and go to fat battery models or mods. Ego and its popular clone Riva 510 are the most popular fat battery models. And re battery life. When you see the mah of an ecig battery - 100mah is about 1 hour of moderate vaping (or more time if lightly vaped, less time if heavily vaped). So 180mah battery is about 1.8 hours of moderate vaping. 280mah is 2.8 hours. 650mah like an Ego is 6.5 hours. etc. So chargers and PCC cases are very important for slime cig vapers.