The ULCS, TLC, the new sea and sea, and i think the new Ikelite all come in pretty much a standard size these days, therefore they are all interchangeable. Personally i use TLC and i love em.
Most improtant, especially if shooting macro as well as WA is to have multiple arms set up. I think a good set up would be 4 inch arms and then a longer arm as well, 12 inch is good but shorter would probably be better for you at first.
If you like to shoot close focus wide angle you need to get the strobes into some fairly strange positions, thats why you want a two part arm as opposed to one long arm.
Watch out for strong currents though, i have had my strobes come back and hit me in the face on occassion in the strong reef hook dives in Palau and Tahiti...