If you are looking to tear something apart to doctor back together it may be worth considering an older Hot Toys body from the military line. I’ve repaired a few knees of my later dated Hot Toys bodies using those as their earlier bodies were made of a higher grade of plastic and still hold up very well today. It can be a pain trying to get legs apart to get the bits of the knees you need and some fall apart when you unscrew them as the plastic is too soft.
As far as a general body, the best I have tried is the latest iteration of the DAM 3.0 body that started shipping with the 78069 Red Wings and 78070 Russian Naval Infantry figures. This a revised iteration that changes the previously non-mobile neck from the first versions. This body design has fixed ankle joints, one less point to be loose and the foot simply pivots around one ball joint that is a solid connection to the leg. For a tighter foot/ankle connection you can swap in feet from the older DAM bodies. Consistency is a pet peeve of mine as I’ve written off boxes full of subpar bodies (DAM included) over the years so I’m glad to see they brought this up to the standard of the final production batches of the 2.0 body which were also very consistent.
The latest iterations of Soldier Story bodies are average at best with some overall inconsistency in the joints. The ball joint hip mechanism tends to fit looser as compared to the Hot Toys style system that DAM switched to and it has a sweet spot where if you rotate the leg a bit too much laterally the leg/hip joint gets fairly loose. Ankle joints can be inconsistent as well due to the design of the lower leg where they plug in as the plastic is soft and can deform making the ankle looser. Easy Simple bodies have been more consistent on later figures but they also have the same issue with the ball joint hip fitting a bit looser, which is more noticeable with their heavier molded boots. World Box bodies tend to be too heavy for their joints. I’m not a fan of their knee joints or their ankle/foot system as it doesn’t mesh well with the heavier weight body they are trying for.