We have both the regular NextFit and the Zip. I like both of them although my husband likes the Zip more b/c of the padding on the waist portion of the harness belt. Both models have the same amount of cushion in the cover and the newer regular NextFits (after Oct 2013) have the same velcro shoulder pads.
My LO had frequent ear infections and threw up a lot so I wished I had the Zip during that phase. It truly is a breeze to be able to zip the cover off easily and throw it in the wash. B/c of this, I would definitely recommend the Zip over the regular NextFit. In fact, I bought one for my best friend's baby and she prefers using it for her newborn over her Britax infant car seat b/c she loves the recline.
Speaking of recline, it has 9 positions. Thanks to this, it is able to fit in many cars. My LO is close to 29 months old and is still RF on recline #2; she tends to nap in the car so #2 is perfect and prevents her head from falling forward.
Installation using SuperCinch LATCH tighteners is so awesome! What I do is LATCH #2 first but don't tighten yet, then LATCH #1 and tighten that side first. Walk back over to LATCH #2 to tighten; I can get it so tight that the car seat doesn't even budge...sweetness!
I've read around on here that the NextFit has one of the highest harness slots but I can't remember the exact stats; I want to say the height limit is 49-50" tall. I know the weight limits though lol; RF from 5-40 lbs and FF from 22-65 lbs.