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Certain knives are going to have certain compromises.
6.5" - 7.5" (maybe/sometimes 8.0") knives seem to have a pretty good balance if still needing to chop. They are not as good at heavy duty chopping as larger knives, but they will still chop. And this size is much more capable at a much larger variety of tasks.
If not needing to chop, I still prefer 4" - 5" blades.
Big 10" blades are really pretty darn narrow focused: chopping. They can muddle through "some" other tasks, but they really aren't too great at most other tasks. 10" and larger blades are just too long, too heavy and too bulky for most knife usage tasks short of chopping and whacking.
I generally think the best two knife combo is a 4"-4.5" knife and a 7" - 8" knife. Both sizes can still do multiple tasks.
Still, if you want the best knife for chopping, it is VERY hard for ANY 7" - 8" bladed knife to compare to a well designed 10" chopping machine like the DF.
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personally for me a two knife combo would be a hatchet/hawk and a 4 to 5 inch. I'd much rather have my RatManDu and Crash Axe than one 7 ich general purpose blade.