Hands down:
1) My girl - Temps
2) Ain't too proud to beg - Temps
3) Can't help myself - Tops
4) Heatwave - Vandellas
5) Stop in the name of love - Supremes

Pretty much...play ANY of the above artists and you will be a hit. But remember - Motown is a label, and NOT an era. Michael Jackson, Stevie Wonder & the Commodores are also a part of that history.
Most people want the 60's stuff when they ask, though. At last check ... "Endless Love" was the biggest selling Motown hit.