Joye 510 or Ego are the only popular models Joye makes. The 306 is something people use the atomizers of but it's not a model people actually buy.
Whatever you get, if you get slim ones I recommend manual batteries. 510 manual batteries are totally sealed on the threaded end so you cannot damage or kill them with juice leaks. And manuals make it easier to get a good drag. Most here use and recommend manuals. And I recommend BOge cartomizers (slim 510 can use the 3 ohm, fat battery Ego can use the 3 ohm or the hotter 2 ohm). NiteLiteVapor.us is the only place I know that sells Boge 3 ohm cartos in 3 colors - white, tan, black (everyone else has black)
100 mah is about 1 hour of moderate
vaping
Joye 510 180mah (and about 100mm long with a carto)
Joye 510 mega xl 280mah (and about 128mm long with a carto)
(both of the above are about 9.2mm diameter)
Joye Ego 650mah+ and 14mm diameter or larger
both also come in "-T" tank versions which seem to attract new vapers but many end up switching to cartomizers.