Don't know what your camera and housing setup is like, so it is hard to give you a definitive answer.
I was shooting with a Nikon D2x in an Aquatica Housing with two SS200 Sunstrobes which were upgraded to DS200 Sunstrobes at the factory with an electronic dual sync cord, fed through the Ikelite iTTL converter into an Ikelite bulkhead.
I have since upgraded to a Nikon D7000 with an Aquatica housing and fibre optic bulkheads with Inon Z240 Type 4 strobes.
My observations concerning the two setups to date.
Big difference in TTL exposure limits between the Sunstrobes and the Inons in favour of the Inons. White underbellies of fish almost always burnt out with the Ikelite strobes but are handled very nicely with the Inons. For my purposes, I find the Inons to be more accurate as far as TTL exposures are concerned. Flash exposure compensation is more discreetly performed using the housing controls with the D7000 and Inons, although you can still reach up and adjust strobes individually if need be.
Loved the colour of the Ikelites and have used theatrical lighting gels behind the diffusers on the Inons to warm them up. Setting the camera white balance to "cloudy" also can help, but I rarely do this.
No more heavy gangly cables to deal with, although I sometimes worry how robust the fibre optic cables are. So far nothing to worry about here. Have tried using an electronic Sea n' Sea dual sync cord with the Inons and don't like inserting the cords into the flash unit at all. Pins in the Inons are very thin, fragile, and easy to break as has been my experience. Have since stuck with fibre optic on the new housing.
No more proprietary battery packages. Have had to rebuild my Sunstrobe battery packs a couple of times as the price of new ones is a little to much to bear. I found 2500mah AA type batteries for the Inons and now recharge about 75% less than I did with the Ikelites. In practical terms, I am now recharging batteries every three to four dives with the Inons instead of after every dive with the Sunstrobes. I do monitor the charge in my batteries with a pulse load multi-battery tester and now only re-charge with they drop below 40%. Also AA type batteries can be found almost everywhere around the globe so when the batteries do fail, replacements are not hard to come by.
Size and weight. The Inons are about half the weight of the Sunstrobes above water and are about twice the weight of the Sunstrobes below water. The Sunstrobes are positively buoyant underwater and Inons are negative by about a pound or two. I have added Stix floats to the arms to counteract this. Traveling with the Inons gives me an extra 4 pounds of baggage which by some airline standards can amount to as much as 10% of your allowable total. Not an insignificant amount these days. Smaller and compact means less stuff to drag through the airport too.
Usability. Hands down to the Sunstobes. Minimum controls mean minimum configurations. Plug them in, turn them on, and your in business. With the Inons you very quickly get the impression this is a strobe the designers made to be all things to all people and there in lies one of it's major weaknesses. It can be too damn confusing. And the owners manuals (not one but two!) is one of the most poorly translated and written manuals I have ever read. It's a struggle to read and not much to be gleaned from it. I would recommend not buying the Inons immediately before a major trip because of the complexity in configuring the strobes. You do need to spend some time with them to get the most out of them.
Bottom line for me. The Inons are not as powerful as the DS200s, but the additional features offset the loss in power. The DS200s now sit on the shelf (one of them is not functioning again). I could convert them to fibre optic with Ikelites new converter, but am not even considering that yet. The Inons are now my "go to" strobes. They may not be as powerful as the Sunstrobes (by about a stop) but the other advantages of the Inons keep me going back to them.
Hope that helps.
