Tysons Corner has absolutely no redeeming features. It's a series of giant shopping malls with horrendous traffic (which is largely true for most of DC area).
It is now a stop on the new Silver Line - 25 mins (give or take) to the centre-ish of DC (Foggy Bottom or Farragut West stops).
Bethesda does have some redeeming features (relatively speaking). It's actually walkable. There are plenty of restaurants and bars.
It is on the Red Line ... straight shot down to DC.
DC parking is a nightmare ... I would leave your car behind if you are staying.
Can't speak to Shenandoah and tree colours ... though I'd be surprised if they are close to or at peak given how hot it has been here of late ... still feels like summer.