One thing I have learned in diving 2 different units (in several different configurations) is that WOB can be significantly impacted by the divers trim and positioning. At least one of my units breathes very easily if I am horizontal (which fortunately is 90%+ of the time) but breathes poorly if I'm in or near a vertical position, like on the surface. It makes waiting for a boat to come pick me up less than fun. Another unit I dive regularly does not have this issue, but one configuration of counterlungs is significantly easier to breathe and is much more comfortable than another.
There is a significant learning curve to diving any rebreather, and just because you're competent on one unit, that does not necessarily mean you're going to be good on another. Each unit has it's own idiosyncrasies and even a minor difference in setting the unit up might mean a big difference in both WOB and comfort level on the unit.
Something else to consider when choosing your first rebreather that has not been mentioned. It is definitely a positive thing to have a local network of divers on the same unit. Obviously you will learn from your instructor how to set up, break down, care for, and dive your unit. However you will not learn everything. Having a local network of quality divers experienced on your unit will help you with all the little things that your instructor may not have told you. Things like setting up your unit for local diving conditions, lessons people have learned "the hard way" over their time diving the unit that you do not now have to learn the hard way, second sets of eyes to help you set up the unit when you have questions, and a local network of divers who should be experienced in fixing the inevitable little things that pop up and have spares on hand is a huge benefit. Of course I did it the hard way, luckily my instructor (as any good instructor should be) has remained available for me over the years, both for additional instruction as well as help with questions I have had in the past.
Choosing between an eCCR and mCCR is a big deal. For me, I chose an mCCR as my first unit because I know how my mind works and I was very concerned that I would quickly become too 'trusting' of the unit and would not pay close enough attention to the important things. Diving an mCCR means that you absolutely must pay attention, all the time, or things will go badly. I didn't get on an eCCR until the proper habits were imprinted to my brain. I still check my computer regularly when diving an eCCR, even if to just satisfy the part of my mind that tells me to check it. Knowing how attentive to details you are, how your mind works, and what your tendencies underwater are all play a part in your choice. It is definitely not something to take for granted in your decision.
The instructor you choose is another huge factor. Being able to communicate with your instructor before and after class is important. How well you are able to learn from him (or her) is also big. Some people are just easier to learn from and some people don't pair up well as student & instructor. How well does your instructor know the unit? Not just the assembly, disassembly, and operation, but the intangibles? Every unit has things that are different than other units, little things that are very important. Can he/she teach you what those things are and why they are important? Can they look at how you dive and help you learn to dive the unit properly? Have they had issues, incidents, accidents, mishaps and are they willing to discuss them with you, as well as what really caused the problems?
The other thing I would consider is how easy is it to contact the manufacturer and actually speak to someone? Both the manufacturers I deal with have always been very responsive when it comes to questions, concerns, ideas, or really anything I have brought up. Sure there have been issues, we are dealing with human beings after all. But from the very beginning of my interactions with them, I have found them to be very helpful and professional. One has gone over and above what I would expect from a manufacturer, especially given that I bought the unit second hand. The level of service I have received from them on this unit significantly exceeds what I would have anticipated.
I know there is a lot to think about when you're choosing a unit. Do your research, ask questions, and make the most educated decision you can make.
