The very first consideration, when choosing a DCC system, is....What system is your club using, or thinking about using.
If you do not belong to a club, then, what is your level of "computer" expertise?
Finally, what are you expecting from your DCC system?
Obviously, if you are a club member, Your club's system is the one to use. You will have a compatible throttle, and will be able to learn the system more quickly, having multiple places to operate it. Throttles do not go from one system to the next. Decoders are universally compatible, throttles are not.
"Computer expertise". If you have had no exposure to computer basics, you will find some DCC systems very confusing to install/operate/program. You should select one that is "most user friendly" (currently, that would put Digitrax at the botom of the list, their manuals require a little computer savy to understand. I have Digitrax, and I don't have too much difficulty with it.) The older Soundtraxx decoders also require some understanding of the Hexidecimal number system, and bit weights, in order to be efficient at programming them.
"expectations"....Outside of club membership, this is the important one to consider. Will the system you are thinking about buying, do all the things you want a DCC system to do.
For example, to my knowledge, Digitrax is the only system that puts two independant "throttles" in your hand. All the others require changing selected loco to control a second, independant engine, or train. I like to operate a train, with a helper on the tail end, without having to change speed tables, to permit consisting.
I would highly recommend visiting a hobby shop, where you can operate several different systems, to see which you are most comfortable with. The shop where I work has a test track that can be quickly configured to operate DC, NCE, EZcommand, and Digitrax, including the "jump feature" of the Digitrax Zephyr system. Not only does this allow demonstration of DCC, it also permits DC, and DCC operation of locos equipped with sound units, so the customer can see the operating differences of the two environments.
Pete