Slim 510 comes in 180mah and 280mah (100mah is about 1 hour of moderate vaping)
Slim 510 can only use standard resistance atomizers and cartomizers, not the hotter LR ones and they also cannot use the Ego or Riva 510 fast charger cable.
If you get a slim 510 I highly highly recommend manual. The manuals are sealed on the threaded end, very safe from being damaged by leaks, and you can use a drip tip on the atomizer with manuals. Manuals also generally make it easier to get a good hit.
I do not recommend the 510-T tank model because it is starting to seem like their batteries and chargers may be reverse polarity and incompatible with standard Joye 510 and compatible 510 batteries. If you want to try tanks, you can use a 510-T tank atomizer and tanks on a normal 510 battery.
I do recommend you buy Joye brand to avoid the one or more reverse polarity clones.
Ego and its popular clone Riva 510 - 650mah and up, fat battery manual ecigs. (see Liberty-Flights.com and press the 20% off upper left front page then look at the prices now that they are reduced). these fat battery models can use standard resistance or the hotter low resistance (LR) atomizers and cartomizers (LR uses the battery charge up faster)
How to avoid the annoyances of atty+cart?
On manual batteries you can use a drip tip and atomizer for testing juices and some vaping (on manual batteries only)
And use cartomizers! A cartomizer, if used with appropriate juices and kept damp, may work well for a week or more. it take the place of the atomizer and the cart, holds more juice, needs juice less often, provides a more consistent vaping experience.