It all depends on the style of smoking you do, the level of nicotine that will work for you.
Many start with small kits like the AIO and similar devices...
Some prefer going big right away with removable batteries and tanks, so that they can grow if needed... o rjust have something more powerful as a "just in case". The advantage in going for such a device, is that a decent mod like this could be fine for a very long while and you can try different tanks until you find the one for you. Also, with a removable battery, should it die on you (the battery), you pop a new one in and the mod is good to keep going. And also, a "full mod" will have various options such as temp. control and other stuff
The sealed mods/battery type, once the battery is dead, the whole mod is a paperweight. But the advantage with those, is that they tend to be smaller and more discreet and portable and quite fine for many. Plus can be much cheaper. (as some end up losing them, or dropping and breaking them, and it's not a big loss)