Opinion: best value HD truck under 20k?

Diesel:
ford 2000 - 2002 buy the standard transmission
dodge up to 2007 buy the standard transmission

Gas:
Ford V10 - all good, but 3 valve and 5 speed auto are better
Ford 2011+ 6.2L gas with 4.30 rear end
Chevy 2007+ 6.0L 4.10 rear gears and 6 speed auto.
Ram 2011?+ 6.4 Hemi

I don’t know a lot about the chevy diesel trucks, so it’s hard for me to comment on them. I’m sure they are good and I hear the Allison transmission is also good.

Since you didn’t specify gas or diesel and didn’t say what you will be pulling, I would say a single rear wheel F350 crew cab long bed 2011+ with the 6.2 gas and 4.30 rear end. I’d buy a white one with cloth seats. Watch for high engine idle hours when you shop.

I wouldn’t be concerned about brand. I’d look for low miles and complete maintenance records.

The Ford 6.0 has a bad reputation but there are many people who say they were not that bad. The 6.4 was better. The 7.3 was good but very hard to find. The 6.7 is excellent but I doubt you'll see one for under 20K. Of course maybe you are looking for a gasser.

A 2017 Chevrolet Express 3500!

The 7.3l diesels seem to have a huge following.

If you haven't checked the prices be prepared for sticker shock. Otherwise the only answers you will get are: "my truck is better than everyone else's"