I personally use the Smoke51 product and have had great success and enjoyment with their use.
I too, when looking into a "cigarette style" electronic cigarette, was impressed with their design, and especially in the 2 piece set up with disposable cartridges that contained the atomizer. Meaning, I had a new atomizer system each time I changed the cartridge.
I have also found that I can "drip" the Smoke51 cartridge with e-juice to both extend their use and to obtain more flavours which was a huge plus for me.
You'll find them to be the most expensive of the bunch, but you pay for that convenience as well as the style. So, if your set on "that" type of unit I can honestly suggest you try them as I have.
If you review this forum you'll also find what appears to be a lot of good user reviews of the pen styles. Users of those types claim better vapour, hit, and taste, but I cannot comment on that as I have not yet tried anything else.
And if Smoke51 continues to treat me as they have to date with any questions I have had, and a decently quick product delivery, I may never bother to try anything else.
Thats my personal 2 cents (and I guess a plug for the '51, lol), and I suspect others will chime in with their opinions shorty.
Vape On,
Greg