The Kohler Command and Command Pro are great engines -- high-quality and include better bearings, hydraulic lifters, oil coolers, etc. Their Courage (economical) line carried some of these features but had a number of quality issues. That's probably why you are seeing the "7000 series" as they ended up going with a new design. (NOTE: My lawn mower has a Courage engine and it's seen 6 years with no problems)
In the past, Briggs' higher CI engines left a lot to be desired but I've heard they've made great strides in recent years.
This post was edited on 3/3 at 10:42 pm