I'm basing my views on the demos that I heard at motifator.com. all those numbers the motif ES has are great. But,

1- The fantom never ran out of polyphony and I like to use allot of layers.

2- Navigation are easy and awesome in the FantomS and I tried the original motif and wasn't impressed with the OS and from what I heard(from yamahaUS)the OS of the MOTIF ES is the same as the motif.

3- The SRX expansions are great and you have 9 of them to chose. and you can add 4X of them. should try them if you get the time.

4- The fantom loads your samples when you power up which is a plus comparing to having to load up samples every time you have to power up in the motifs.

5- The MotifES can hold 512MB of samples which is great but it's RAM not ROM and if you want to save it, smart media cards can hold only 128MB so you can't. what's that you say? USB? well you need a computer and you need TIME. AND enjoy the Awesome sample transfer time that Yamaha has(way slow!). can't understand why they didn't have USB2.0 built in it?

I can go more but really it's all an opinion thing and what your needs is and personally the FantomS suits me.