Haven't read all the way through this, so it may have already been mentioned.
My vote would be the late 80's-early 90's Diamondback MTB's: with the horizontal top tube and small diameter steel framing- before small front chain rings became a thing.
I actually had one that fit me at about 22-23", and it was wicked fast. Had to be careful with the thumb wheel shifters though- they turned easily, most times when I didn't want them to.

The other would be late 50's, early 60's CCM full sized men's coaster brake bikes. Some came with the pinned cranks, which were actually an improvement over the previous one piece systems. The cachet here was pricing- they were affordable enough that there were a lot of them around, and practically indestructible as well.

-D.S.