Alternators Smokescreen will always have a special place in my heart for being the figure that pulled me back into the hobby.
Pretty much any of the Alternators, as the whole line remains to this day one of my favorites. As Lastmaximal said, the Ford GT is one that immediately comes to mind as a high point for the series.
Netflix Bumblebee is finally the official Volkswagen G1 'Bee that I had been wanting for nearly 20 years, with the one very slight nitpick of needing a less dour face.
Volvo Prime, specifically the Christmas version, is beautifully absurd in a way that tickles my fancy.