Can't decide which to use MTH Z-4000 or the Lionel ZW?

A modern ZW will allow you to control the output to the track remotely, up to four seperate blocks.  You can also buy a remote commander for a Z-4000 for remote throttle control (independant of DCS). 

Z-4000 is a nice transformer with a lot of nice features, so is a ZW.  Z-4000 has an amp and volt meter built in and has macro button's to support conventional programming of PS-1 and PS-2 loco's.  It's physically large and only has two variable tap outputs.  Z-4000 requires a Remote Commander set to support remote throttle without DCS.  New ZW can handle four variable taps and 180 watts out of each one.  You need a CAB-1 and Command Base to do remote throttle operation.  If you are running predominantly in a command mode, both are overkill.  They go for around $360-$380.  PowerHouse bricks go for around $80 each and each one will provide 180 watts of power.  If you already have a DCS Remote and TIU, I'd look real hard at using bricks to supply raw power.