All three phones are great phones. All three have their advantages and disadvantages. The iphone would be a direct replacement for your ipod. It would connect to itunes and get all your music perfectly, but you would be locked down to apple apps (which there are a LOT) and unable to make your phone personal. And if you are in an area that has it available, this phone does ot have and will not have 4G LTE!
The RAZR is great hardware wise, but it has (as of now) a locked bootloader which will limit the development to some extent (Rumors still float that Moto will unlock, but who knows) Its running Gingerbread which is very solid on the moto phones, and it has MotoBlur ( or whatever they are calling it now) which is really a pretty good overlay. Many folks on the Droid X like the latest version of it.
The Nexus is also great hardware, but you get the latest and greatest operating system and faster updates from google. It is straight android with no overlays, but it has an unlocked bootloader (as far as we know!) and will have a lot of developer support. more options for customization right out of the gate.
Making your choice between these three great devices is really your personal opinion. you should go to a store or use a friends device when they are available to see which one you like the most!