Get the device you think will fit your lifestyle best. With AB's Neptune, no casings/pouches needed to make it waterproof. Just make sure it's in its waterproof configuration (Control off, different cover on, and use the AquaMic with it). Ab also has its own casing in the work for the Naida Processor to make it "waterproof" too.
AB's capabilities and resources are currently at 25% capacity, so there is still tons more room for further improvements. Med-El is at about half (50%), and Cochlear is about maxed out unless they can develop a new chip that is capable of plenty more new upgraded improvements. AB and Phonak are under the same roof, the same technology in the Phonak hearing aids have been incorporated into the AB Naida CI (can use Compilot with both Naida CI and Naida HA if one is bimodal) and has some of the same features that the hearing aid provides, which is pretty cool. If one chooses to go bilateral and get 2 Naida CIs, it won't matter which processor goes on which ear, it'll recognize which ear it's on and pull up the correct programs to use for that ear (Cochlear and MedEl's processors are only just specific to the one ear it's programmed for, no switching ears). T-Mic capabilities, putting the mic in the bowl of your ear for more natural hearing, as compared to the mic behind the ear on a Cochlear processor (can even use T-mic with the Neptune if you get the T-Comm accessory). There are loads of differences between Cochlear and AB. AB also has paired simulation or individual simulation of the electrodes (which gives the patient even more options for processing strategies). AB has ClearVoice to help in noisy situations, and with the Naida it has the Zoom features which I've heard works better than Clearvoice even. There is also Optima, which can double the life of battery use on an AB processor as well.
I have AB and am far pleased with it. Sure wish I could get the Naida, but not eligible for an upgrade. AB also has newer processors in the works to be released either later this year or next year (seems to be a new processor on a yearly basis for the next 2-3 years).
I'm sure Cochlear is a good device too, but I just personally feel AB is better than Cochlear, technology wise. But that's just me.