I bought a 2020 Custom Trail Boss in April. I owned a higher level trim SUV prior. Several friends & family have LT or LTZ trim Silverados.
Bottom line, I love my Custom!
I was a replacing a non-Chevy full size SUV that served our family very well, but finally wore out. I wanted a truck to take on some rough fire road to go camping, fishing and shooting. I also had a limited budget from my wife. My priorities were getting a V8, 4x4, and I really liked the Trail Boss suspension and tires upgrade over the regular Z71 package. I chose to spend my money on those features and extending the warranty in case I break something "on paved roads" rather than a Z71 LT trim. I could get a Custom Trail Boss with V8 for about the same as a 4x4 All American LT.
The most important interior features I was looking for were Apple CarPlay, bench seat in the front to carry 6 people (we are a family of 5 with a dog), and cloth seats.
I agree with what Don wrote above, the steering wheel controls are what I miss compared to the LT. I miss controls of the radio, and answering phone calls. I also miss the controls for the Driver Information Center (DIC). I find that I am often switching around to see the fuel range and tranny temp when I am on a longer trip, or hauling stuff up a mountain road. With the Custom I have to reach through the steering wheel to turn the knob by the gauges.
The other features that are not on the Custom, which I really don't care about, but would be "luxuries" for me are the keyless fob, heated seats, and center bench seat storage. The 8" infotainment screen in an LT has the ability to add an aftermarket front camera to help with parking and driving over obstacles. The 7" screen on the Custom does not. I found a wireless back-up camera/display at Costco that I put on the front license plate for $130 and it works fine for me. The stereo speakers on the Custom are not the greatest, buts still far better than almost every car I drove for 20+ years. I have had cars and SUVs with automatic HVAC, and found that I don't really need it. The HVAC system on my Custom works just fine.
A major factor between the Custom and the LT, at least in the 1500 series, is whether you get the latest technology in the engine and transmission. I was only looking at the V8. The Custom has the older technology cylinder turn off ( I get the letters AFM and DFM confused which is newer) and a 6 speed tranny. The LT has the newer cylinder management, auto engine start/stop, and 8 speed tranny. This means the LT get better fuel efficiency. While I appreciate the better efficiency, I don't drive enough for this to be worth the increased up front cost. Getting the Silverado was already a big improvement over my prior SUV for gas mileage. This may not be a factor in the HD series of trucks because I don't know the drive train options. While I am confident the bugs have been worked out on the new engine and tranny, I wanted to also stick with the drive train that had been on the market for many years. I am planning to keep this truck for a decade or more, and wanted to minimize things going wrong after the warranty expires. So I consciously chose the 2015(?) technology over the 2019 technology
I would still choose the Custom over the LT based on the features that I wanted in the truck. I think this is mainly a personal preference, and knowing what you need. My priority was having a stock suspension and tires that could make driving on fire roads more fun and comfortable, hence why I got the Trail Boss package. If you are getting the HD package, I am guessing there is a lot of payload and towing for you. I did not prioritize the interior amenities or the latest technology in the engine and tranny.
The Custom has all the amenities I needed, and no surplus. I think it is a great trim level, and keeps the truck feeling like a tuck to get dirty and have fun in. I didn't want it to feel like a Cadillac that you obsess to keep perfect.