Of the units that have been discussed, I'm certified on a Meg, JJ, Fathom, KISS Classic and for full disclosure sake, I'm an instructor on the Fathom. I'm not certified on an X and I didn't sleep at a holiday inn express.
Meg - pros: large amount of support worldwide, stable platform, replacement parts are relatively inexpensive. Relatively easy to de-water. Comes with both a HUD and a handset by default. Cons: Apecs 4/Meg 15 electronics were glitchey, the older 2.x were more stable and of course the Tiburon w/Shearwater is an improvement. Chestmount CLs unless you go off-stock, supposedly factory BM counterlungs will be out any day. $$$.
JJ - pros: relatively simple platform for an eCCR. BM CL's. Build quality is phenomenal, ability to easily reconfigure for BM bailout, relatively decent distribution. Relatively easy to de-water, but there's a note about that in the cons. Comes with both a HUD and a handset by default. Cons: weight. the head attachment mechanism lends itself to getting jammed up with debris (push down on the head, then pull up). limited scrubber options without replacing the can (however, the stock scrubber is still suitable for 5-6 hours!). the water dump is on the wrong side of the counterlung, you have to go feet down to clear it. Some "stock" units only came with an ADV instead of an ADV and MAV, but my understanding is all units now come with the DIL MAV as well, so if you buy used you may only be getting a unit with only one way to add gas. I think the counterlungs are a little small for very big people.
Fathom - pros: very simple platform, incredibly easy to work on, clean and rebuild (dump the head in a bucket of water, come back in an hour). BM CL's. Build quality is exceptional. Relatively easy to travel due to weight and size. BOV is stock. I'm a huge fan of the needle valve. Comes with both a HUD and a handset by default. The new HUD is fantastic. Easily convertible between BM bailout and SM bailout. Cell placement is designed so water does not drip on the faces, and a DIL flush blows gas across the face of Cell #1 for instant validation / drying. Easy to de-water / water trap. Designed for off-board DIL by default, but easy to convert to on-board DIL. Cons: The two scrubber options are both radial, I wish there was an axial option but there can't be because of the gas path on the loop. Limited distribution, there are only ~60-70 of these in the wild, but they use JJ cells, standard "weed whacker line" and Shrimp mushroom valves, so most "user replaceable parts" are easy to find. The only ADV option has some issues, blocking it off on descent can potentially cause it to collapse, flooding the unit - I no longer recommend an ADV to people buying a fathom and I removed mine. I know someone that flooded her Fathom this way. I think the counterlungs are a little big for smaller people.
KISS Classic - pros: relatively simple platform, you can get most replacement parts at Home Depot. Cons: expensive for what it is. Cell placement has the cell faces down, if you lean back water will drip over the face and cause your cells to go haywire (yes, I got to experience this a few times). Counterlung placement was a pain in the butt, I wound up hacking up my KISS frame with a dremel to make it easier, and about six months after they released the explorer frame which basically did what I did with the dremel. Only comes with one monitor by default, you can add a secondary (HUD, NERD, etc) for more. You can not de-water the unit, period. I really have a soft spot in my heart for the KISS, I have a little over 350 hours on it and did some neat dives, but I wouldn't buy a new one. If one were on the market used for a low price, I'd probably look at it.
X-CCR - pros: based on the Hammerhead platform, so plenty of scrubber / can options. Relatively simple to de-water. BOV is stock. Shearwater electronics. Both HUD and handset by default. Cons: lots of extra electronics (CO2 monitor, pressure gauges and some other stuff) may cause issues (however it seems stable). Rechargeable batteries in the head (I'm not a fan). The ADV has some issues, blocking it off on descent can potentially cause it to collapse, flooding the unit - I don't think there's an option without the ADV. I know two people that flooded an X-CCR this way.
All of these units have pros and cons, none of them is perfect, but in my opinion, all of these units are very diveable for most people and most diving situations. If I were buying a brand new unit, my number one pick would be a Fathom, especially if I wanted an mCCR (but remember, I'm an instructor on the unit and so I am biased with a financial interest), and if I wanted an eCCR it would be a toss-up between a JJ and Meg/Tiburon (and I'd probably lean towards the JJ). I think the X-CCR is a bit overkill.
Not mentioned, but also units that I've got experience/training on:
Defender - I like this unit a lot. I worry about the future of the electronics and support for the platform.
Optima - I like this unit, and I recently purchased a Choptima, which I like too.
SF2 - Sigh, there are things I really do like about the SF2, there really is nothing that de-waters better and it is incredibly simple to build/tear down. Cons are I'm not sure what the future support in NA is going to look like and it only comes with a single monitoring device; the sidemount unit doesn't even come with a fischer to add a second. The used market has cratered in the US, you can buy one of these in great shape right now for half of what dealer cost was just two years ago.