doing Belize by liveaboard (see my previous post regarding that) vs. doing Cocoview.
I believe you also like the Nekton, as do I.
The Belize Nekton vs CoCoView?
It's a draw.
I can't remember (any) dive site name, much less the ones off of the Nekton, but I found their Belize itinerary to have very similar diving. Because of the moorings, for many divers, the Belize dives invite you to dive deeper. Most folks look at the mooring pin and dive the wall
below. I almost always went up & shallower from there. The bubble watcher laughingly remarked that they thought "we were making a beach head landing" as they watched our lights at night. Many divers have limited deep 50 minute BT's, we poked around for 70+ BT's.
We like variety - spur and groove, walls, swim-thrus, wrecks, deep, shallow...
They took us to only one Belize dive sight of remarkable architecture approximating a spur and groove, but on a huge scale. Although they do now occasionally do the Blue Hole which I see as of limited interest, the rest of the diving was architecturally unremarkable. There is certainly great drama in the Belizian walls and sloping sand fields, but spur and groove- not so much.
Swim throughs, I'd give it to CoCoView. Mary's Place, Calvins, Two Tall, Hole in the Wall (South side) and more. There are chimneys at Doc's Dive that you'll have to search for and do on your own- they are extremely advanced (snug) and they are not guided. On a similar note, Mary's Place is not just the guided tour- there's lots more to explore there if you have the itch. Scutt's Slot and Lita's Hole lie nearby.
I think the Nekton might suffer from it's one strength. Local resorts and their DM's know every nook and cranny. They know where the holes and swim throughs are. The Nekton may not make you sit through a thirty plus minute ride out to dive a reef, but their internal knowledge of the the many reefs that you will likely see is slightly less. Is that a real downside? Never bothered me.
Wrecks? Roatan South side wins again. Not only is the intact 140' tanker lying in 35~65fsw calling out to you, but there's also a boat dive to "Mr Bud", and intact Shreimp boat placed in 55~65fsw near French Key. It sits in a sandy basin atop a vertical wall.
Deep? Well, you can do it either place, but I think that due to the way the Nekton pins are situated, you'll have better access in Belize. Both islands feature the same South side structure... they are the exact same continuous geological reef structure, after all.
Any of these islands have fringing reefs that begin near shore. They break in a very shallow 10~40 feet and drop vertically to sandy plateaus in 70~90fsw. The next wall breaks at that depth a ways seaward. That second ledge is the place that Nekton drills it's mooring pins- likely at 70fsw. The Roatan South system is set upon the first of the two breaks, so most are in 35fsw.
In Roatan, you have to intend to get deep, in Belize (from the Nekton pins) you have to plan to dive shallow. Both destinations offer either.
In life, if you can, one should do both of these excellent choices.
) and feeding it to a 10'+ long Green Moray. I know they don't grow that big, but we measured it and you can argue that with him. This Parrotfish measured 18". The Moray swallowed him in one gulp. 
