Braid or no braid?
Depends...
Braid is more supple. There is basically no memory in braid. It also has no stretch. All three factors helps to provide you with greater contact with your sinker and bait, allowing you to feel the bottom better and feel subtle hits. This is why braid has better sensitivity.
Due to the greater strength in braid, you are more capable to pull out sinkers and hooks from snags. Channel Catfish likes to live in snaggy water. This helps you to retrieve more rigs and save money your pocket.
At the same diameter, for example 30lb braid vs. 8lb mono, braid allows your to increase strength without increasing diameter. The lower diameter allows you to cast further. In a river situation (Channel Catfish loves some current), the lower diameter cuts through the current much better. If you were to use 30lb mono, the thicker mono diameter would create a lot of surface for current to push against that line. This causes drag in the line. In order to compensate for this drag, you need heavier sinkers to keep bottom position. Heavier sinker equals more chances that you will get your lead snagged (bigger size sinker...more volume...less likely to be pulled out of a crack between rocks). The greater drag also cause your line to bow, increasing the slack in the line to decrease sensitivity.
But...braid is more visible you say...
If visibility is an issue. it can be easily overcome by adding 3 to 4 feet of mono or fluorocarbon in front of the braid. This is your "topshot" (technically, such short addition of mono or fluoro to braid is really a leader...but to make it less confusing, I'll use the term topshot. But a real topshot is usually much longer). Use a slim splicing knot so that you can potentially reel the knot into the guide (or simply don't) without interfernce...and be able to cast without the knot getting stuck in the guides. This length of "topshot" is enough to prevent fish from seeing your line. Be realistic...most Channel Catfish habitats are turbid rivers. Visibility is less than 2 feet most of the time. They are not going to see your line that easily if you use a 3-4' "topshot".
You can still use a heavier mono (15-20lb) as a leader to maintain the strength of your entire system, without sacrificing stretch, diameter, and suppleness. But you gain abrasion resistance and stiffness to your presentation. Let's be honest, 8lb is not very abrasion resistant.
Why stiffness, you say...
In a current situation, a bait such as a whole worm, a chunk of cut minnow or sucker, or a chunk of liver will roll and flutter in the current. The longer the length of line between the sinker to your hooked bait, the more your bait would roll in the current. A bait that is constantly flapping in the current, under a turbid situation, is much harder for a fish to find your bait. Just imagine if you have an 18" hook leader and the visibility is only 6", your bait is allowed to swing around out of sight of an interested fish. You are decreasing your chance that a fish will find your bait even if it had already homed in on the scent trail. Speaking of scent trail, a stationary bait that sits in one spot on the bottom produces a more concentrated scent trail than a bait that flutters around dispersing the same volume of scent over a wider area. Yes, you may attract fish from a greater area, but that scent is also less concentrated (fainter) thus harder for the fish to locate your bait.
The stiff line, in conjunction with a shorter distance between your sinker and your hook, helps to reduce this fluttering of your bait in the current. With a short 6" length of 15lb mono, you can be pretty sure that your bait will sit much closer to bottom and tends to roll less. I haven't found Channel Catfish to be wary of sinkers, so the proximity of the sinker to the baited hook doesn't seem to deter a Channel Catfish from biting.
Having heavier and more abrasion resistant mono closer to your hook also helps to address the very rough sand paper teeth of bigger Channel Catfish, and their habit of running along the bottom in and amongst rock. This will help reduce the number of line failure. If you feel heavy mono is too visible, then use heavy fluorocarbon instead.
