Which units are good in tank reapers company and what units are better in rifle training companies?
Rifles are good with rifle training. Bars are buffed by this as well, so worth getting.
You'll need to have AT though. The best american AT is still the 57mm and the vet 2 sticky range, imo. If you decide to spend fuel on AT the sherman upgun or the m10 are good options.
For reapers, sadly the best way to go about with this seems to go with a lot A LOT of zooks and possibly 2-3 at guns. This will give you a huge reserve of heavily buffed AT versatile, accurate and damaging against any type of axis armor or vehicle. Sticky's are still recommended as they are buffed and a core american at ability.