They are all good and then there are some that are bad.
The truck that I had to do the most work to was the 02 7.3. But I kept it the longest and I could do the bulk of the work myself. Injectors, glow plugs, GP relay, the wiring harness up under the valve covers. The engine control module was the only thing I paid to have fixed and I think it was the wiring harness anyway because it still acted up after the ECM was replaced and stopped after I replaced the wiring harness, this is why I hate paying people to fix my shit, I can throw parts at it much cheaper than a "mechanic" can.
The 6.0 I had was great, 100,000 miles and the only problem it had was an EGR valve and it was replaced under warranty. Way more power than the 7.3.
I have a 6.7 now and it has been almost 100%, well after I hit that big bump and some parts fell off from underneath it has been 100%.
Rev has a 6.4, and after he hit the same bump I did, it also has been a great truck with almost 100,000 miles.
Go with what you can afford.