I’ll pick one per decade.
1950s: silver Mercedes
1960s: orange McLaren
1970s: Ferrari 312T
1980s: JPS Lotus
1990s: Rothmans Williams
2000s: Brawn BGP001
2010s: bumblebee Renault
All-time favorite: Rothmans Williams. Funny, as I never really rooted for them. But their livery was a total beauty. The choice of the 312T might be a bit of a surprise, but it paid great attention to detail and had a lovely design.