Living underwater does steel too, and I believe someone else does LP steel...but I can't recall who. Our last trip we dove with Aldora and Dive with Martin (4 days each). The steel tanks take some getting used to, and I found that with a 3/2 full suit and booties I didn't need any extra weight...but not having weight in my front pockets made the tank want to roll me. Its not a problem, in fact I like the bottom time so much I think I may stick with the steel tanks from now on...but I did find that my feet were always slowly moving to keep me from going belly up. My dive buddy wasn't as much of a fan of the steel tanks...as she gets cold after 60 minutes anyway (in a 5 mil, booties and a full hood!) plus battling the tank was distracting for her.
We have now dove with:
1. Aldora
2. Dive with Martin
3. Dressel
4. Blue XT Sea
And I would rank them in that order with the following caveats. Dressel has free Nitrox, but they limit your dive time to one hour in the morning dives and 45 minutes in the afternoon. Since my air consumption on a 90 foot multilevel with an aluminum 80 is about an hour anyway...they edge out Blue XT Sea by a nose due to the free Nitrox, cheaper packages, guaranteed afternoon dives and nice boats. Dive with Martin is clearly better than Dressel in our eyes because Dressel doesn't handle your gear, while Dive with Martin will take it back and rinse it for you, set it up on your tanks the next morning etc (same as BXTS), plus Dive with Martin has fruit, bottled water etc during surface intervals on the beach...whereas Dressel hands you a cup of water and takes you back to Iberostar for SI's. That 5 minute boat ride back to dock though has a definite benefit for Dressel.
Aldora was head and shoulders above the other three in both my eyes and my partner. Their SI's are at a beach club where you can get anything you want, there is an abundance of water, long and warm boat cloaks and they handle your gear for you. The tanks are ridiculously full of air and if someone in your boat burns through their tank..the DM has an 8 foot Octo that he shares air with them on. That seemed quite odd to me at first, but having seen it in action it seemed to work very well and every time someone burned through a tank and had to nurse off the DM...their next dive they were more careful and didn't need to again. Spending 15 minutes attached to a DM seemed to show them that they were not paying attention to their breathing, were staying deep too long or needed to hang out a bit shallower..and they asked questions in the boat about how to improve their breathing. Aldora's boats were also the best I have been in thus far and never crowded.
I have to say, my dream op would be Aldora with pairs surfacing as one of them gets low (much like Dressel and BXTS do) instead of the entire group going up when one diver eats a tank in 38 minutes (happened on one of my dives....was an O-ring failure, not the diver's fault)....but still, I was in the boat looking at a Nitrox tank with 1950psi in it....made me want to cry....in fact, I might have shed a tear or two, but I will never admit it. One nitrox tank with Aldora costs as much as a two tank day with DWM, so leaving one with that much air in it is painful. One other small issue is that normally Aldora heads up for a safety stop at 1000psi....which to me is a bit soon on a multi-level dive where you are quite shallow by that time. Other ops are 700psi and up, which I believe is plenty of safety cushion when you are not deep.
Still of the four we've tried...Aldora was the best experience. Despite seldom getting in the boat with less than 1400psi (group surfaces together)....the dives were still typically over an hour. On the last day I was put with a group of experienced divers and when I got in the boat I had 1050psi left and we had done 80 minutes, 88 foot multilevel swimming through palancar caves. It was the only dive I've done in Coz where we swam the entire time, down around and through the large coral formations. Because we were all decent on air the DM said we were going to swim it instead of drifting over it motionless. I very nearly hugged all of those divers when we got out...without question, best dive yet.