The whole CE4 history is a bit confusing, even for those who have been following it for a while. While I didn't try them "way back when", I've heard that the original CE4 was not a very good design, and then the CE4+ was born. In the CE4+ line, there have been revisions with long wicks, better plastic tanks, and different colors, but nothing really improved the performance very much.
The newest versions with the replaceable heads are often referred to as the CE5, Vision 2.0, Thor, and probably a few other names. There were early revisions of these as well before the Thor and Vision 2.0 came out that weren't very good, but since the latest revisions, even the clone makers seem to be getting it right as of late. These are definitely a step up from the CE4+ line both in performance and operational cost, because of the improvements in the heads and the fact that they can be replaced or even rebuilt (if you want to do that).
I don't really know the history of the CE3s, but I do know that the current revision sold at DiscountVapers performs very well and are very affordable. At about $10 for a 5 pack (which includes the syringe), these have a good lifespan with great performance and flavor. Filling them is more of a hassle than a CE5 or Kanger T2, but no more of a hassle than filling a carto (if you use a syringe). My only gripe with these is the capacity, but if you're a person that likes to use different flavors throughout the day, it's easy to fill and carry around several of these to switch out.
