Yeah, that’s a common issue. Some rubber or vinyl parts—especially tires—can have oils that react with styrene and cause melting or staining over time. It’s best to keep them stored separately from the plastic parts.
I’ve built both recently and tend to prefer Revell—better fit and cleaner details. AMT has some great subjects, especially older cars, but the quality can vary. Price is usually similar, so it depends on the kit.