'Back in the day' people bought complete e-cig starter kits like the DSE901, DSE801 or Joye 510 which were completely different models of e-cigs. They still sell them, but more common now, at least amongst experienced vapers is to use the atty's on alternative power sources like "fat batts" or "mods". The DSE801 was one of the earliest e-cigs - a "full sized" model with a large 1ml cartridge, the complete e-cig was just over 6" long. The DSE901 was the "mini" with a smaller cartridge, and for many, was a better all round choice than the DSE801 for various reasons. The Joye 510 was also a mini but was a later, competing model, and had a much hotter running atomizer as standard than the 901, with poor battery life as a downside.
To me, they have slightly different qualities. The 510 for me personally is the hardest hitting atomizer in terms of throat hit. I have also overall found it the most reliable atty (I mainly use the Joye versions, there are a lot of copy's about). Some say it can mute flavours though. The 801 produces a lot of vapour, has a light draw and overall there's a cooler, fairly airy quality to the vapour. The 801's cartridges have never worked particularly well in my experience, but dripped or
juice fed, on a moderately higher voltage (or in LR form) it can work really well. The 901 is said to allow more flavour through than the 510, while still packing a punch (especially in the LR variety or at higher voltage).
There's also the Joye 306, which is an open bridge atomizer that has been gaining popularity recently and uses the same connection as a 510.
These are fairly generic descriptions. The only thing I could suggest is to try different ones for yourself. Adapters are fairly cheap.