depends how many channels you want and whether you want usb or ADAT connectivity
befaco do a 2 channel usb one, expert sleepers do more channels (both ADAT and/or USB) and are often expandable depending on the software you are using and iirc bored brain do one (but that might be ADAT only)
I've got a es8/es6 combo, but I really only use it for audio i/o via usb to my MBP - I do use it for clocking (on channel 3 using a kick sample as the clock from Logic to PNW - using a saved template with the kick sample on every 16th note, so it moves with any tempo changes)
"some of the best base-level info to remember can be found in Jim's sigfile" @Lugia
Utility modules are the dull polish that makes the shiny modules actually shine!!!
sound sources < sound modifiers < modulation sources < utilities