If M20's and Stuarts are giving you trouble you can always try a build with going Mechanized -> Puma. Personally I've found that beating USF in 1v1 usually is easier if you can manage a good first few engagements to prevent Snowballing into a Stuart. Also focus on cut-off harassment to slow fuel gain.
1. Kubel - Surprising effective beyond just capping - use them to do HP damage to Rifle squads pined behind cover or in buildings. You won't drop a lot of models but they'll be weakened and force USF to get Ambu sooner or suffer. (Delaying Stuart) Pair with Strum closeby for tag team fun and fast repairs. Just don't throw it away early.
2. Volks - if you go Volks heavy focus on getting Munitions point early (or both if you can manage). Go Battlegroup after 3 Volks or so and upgrade STGs ASAP on all of them. This can let you bully non-BARed Riflemen early on and flip the script on usual USF advantage of just streamrolling you with Rifles.
Finally you want to play conservatively with your Rakens if you find yourself on the backfoot with a Stuart out and no Puma. Keep either Fausts nearby at all times or a Shreked up Pioneer (don't bother chasing Stuart with a lone Shrek, use it as a screen/escort to limit it). Don't spread out across map too much - focus on holding at least Fuel and one VP - bide your time until you get PZ4 out and can push. Ideally you can catch Stuart before that with a good faust or Cloaked Raken but that always won't happen.
Thanks for the help, ill try some of the tips youv´e given!!
Still a problem with stuart sniping 4 models in a shot tho =/