Compak is a brand of grinders, the k10 being one of the more popular ones on this forum and has large conical burrs. K30 is a model produced by Malkonig, and has flat burrs. Pharos is another large conical, but is a hand grinders.
Coffee grinders typically have 2 types of burrs, conical, or flat. There are some hybrids out there, but don't worry about that right now. You can search this forum for countless threads about the two types, but typically you will read that conicals tend to bring out the higher notes, and flats bring out the low end. Conicals also tend to be more stable in the fact that you can switch beans easily with minor or no adjustments needed.
As for "doserless" or with a doser, a mechanical doser is attached to the front of many espresso grinders, and the barista controls the amount dosed into the portafilter. "Doserless" is really a term for timed or weighed dosing, depending on the grinder. Most are timed (K30, E and F line of Compak, Vario, etc.) but the Vario W can also be dosed by weight. Depends on your needs for a grinder, and your preferences.
Step vs. Stepless - The vario is stepped, macro on the right levers, micro on the left, allowing you to have a "set point" for your grind. With small enough steps, this can be helpful and not leave you wanting an in-between. HG-One 2014 version is "micr-stepped". Most other high end grinders will be stepless, allowing you to set the grinder exactly where you want for control of the fineness of the grinds.
Since you already have a Vario, if you like it, would suggest looking towards an "on demand" or "doserless" type grinder, but keep in mind retention may be higher than what you are used to. The K30 would be a significant upgrade, and would operate somewhat similarly to what you are accustomed to.
It might be a good idea to actually get your hands on some different grinders, see the different options, and figure out what works best for YOU. Just because you are speaking to a retailer doesn't mean you have to make a decision that day.
Figure out what you want, then buy once, cry once as they say...