I've met Francis, the Fish Geek, and he actually knows his fish, and cares about the tanks. Most of the fish provided by either show are wild collected, FTK just acknowledges this fact while ATM ignores it.
I've seen very little of either show, not being "into" TV in the least. But, I've seen ATM put wildly incompatible fish together, massively overstock tanks, and create tanks that are completely unsuitable as aquarium habitats (my opinions). For instance, they created a fish tank in a winery that was shaped like a wine bottle, standing up. The low surface area of the "neck" of the bottle resulted in massive fish die off (a knowledgeable installation would have tilted the bottle to increase surface area). They created a tank with a skateboard ramp on the side of it. Not only did this quickly become opaque from scratches, but fish have never thrived in it, in no small part due to the noise. They have placed decorative elements in to tanks that kill fish.
And while you think they may be creating stable environments with some sort of bacterial product or cycled media, virtually all of their tanks are reported to have massive die offs within the first two or three months. They're generally also heavily, heavily overstocked -- for instance, the "phone booth" tank that they are famous for had at least 20x the number of fish it could support. Further, many of the fish they placed in the tank needed much, much more swimming room than the tank provided.
ATM does not provide continued maintenance services, and will often turn these services over to local companies. I've talked to some of these local companies. ATM creates unrealistic expectations in their clients (Sure, you can keep 75 yellow tangs in a 125 gallon tank) which frequently result in disaster. Most of the fish placed in the tanks by ATM are dead within a month, and many of those clients -- after spending hundreds of thousands of dollars or more -- have the aquariums removed.
To add insult to injury, the aquariums are created without thought to cleaning them. The large, heavy, and often delicate decorations do not hold up to scrubbing, and are often secured to the tank, requiring someone get INTO the tank to clean them. They aren't removable for cleaning. Large sections of the acrylic are often visible, but inaccessible to cleaning tools, which means they'll soon be algae covered.
Their tanks are non sustainable in any way. ATM knows nothing about aquariums past the "set it up and have a spectacular reveal" stage, and cares nothing for the health and well being of the animals placed in the tanks. Other online posts have spotted them placing dead, dying, or diseased fish in the tank -- they have 50 clown fish in a bucket and dump them into the tank, and you can spot that one that sinks straight down. (Though I never saw it myself, the fish in their logo had ich for the longest time).
I've purchased some of the Living Colour decorations used by Fish Tank Kings; they're better quality than the ATM stuff, and a whole lot easier to clean. While that show has its share of manufactured drama, the FTK guys seem to actually care about their fish, and have on staff biologists. Sadly, ratings talk, and the show where a pair of buffoons clown around and break stuff is the higher rated show.
My opinions.
