Heard the same thing. Some customers say the 7.3 pulls like a diesel out of the hole and is getting way better mileage than the 6.2. Long distances pulling a big load the diesel wins every time. Just depends on what you need to do.The 6.6 should be a good engine and should outperform the 6.0 under a load. Better torque numbers. It's based of the LT engines and they've been fairly reliable.
The 6.2 will do everything that the 7.3 does, but the 7.3 will do it better. It's a true heavy duty engine. Good low end torque. A construction company I do some work for has a couple and they have been happy with performance and fuel economy as well. They probably pull 10k everywhere they go though.
If your main priority will be towing power, go with the 6.6 or the 7.3. If you could get by with a 1/2 ton, but want a 3/4 ton for extra trailering stability and reliability b/c you occasionally hook to a trailer, I'd say the 6.0 or 6.2 would be fine.