The single vehicle is the understanding that all teachings are personal advice on how to soften rigid mind-habits, letting go of pointless aims, and then settling into a gentle presence that is both calm and kind. Our attention simply remains for a while in this way, at ease in itself with nothing that needs to be held or cast away. This aware steadiness is often called shamatha, being calm, and it is the basis for all higher or deeper states of authentic insight.
Go for the highest goal, the real deal: full buddhahood in this lifetime. I’m not saying lower goals aren’t needed. The simplest meditation attainments help, of course. However, going for the highest goal opens more possibilities and yields more benefits you are probably not aware of.