Im only gonna give you my experience with the Digital Aquatics Reef Keeper since its the only one i've used.
If you get the elite system you can intergrate with 60 modules.. a module being, 1 PC4 power strip (4 outlets per strip), SL1/2 for ORP,PH, Salinity, Temp.
....
also you can get the NET module which gives you an ethernet port, so you can plug it into a network and have access to it VIA a web interface anywhere and have control over your tank.
Thanks EMU Reef: How was setup? Were the instructions in plain english? Did you have to 'code' your information in or did it have a good interface?