Of those you listed the Lenz is my pick. I have a poll on my blog asking people what the most important criteria is for DCC. Ease of use, expandability and Throttle choice are among the highest.
If it were me, I'd be looking for a used Lenz system, they can be had for about the same price as the Zephyr and IMHO, a better system. With all the religion around Digitrax, I started to switch to the Digitrax Super Chief, actually purchasing one and hooking it up. Ultimately, I saw no advantage and some disadvantages in going to their proprietary architecture. (Lenz is much more open)
Tony's Train exchange has a number of well written primers on DCC including some very comprehensive comparisons of solutions out there. See my review in the product section here at Model Railroad Forums.
Better yet, if you have a friend with DCC, or a local club, talk to them. They are your local source of assistance and you benefit from following their lead.
My 2 cents,
Joe
PS,
Two of the four systems you recommend are built by Lenz (Atlas)
