One set? I collect everything from baseball to pin-ups, so one set...
If I had to pick a favorite baseball set it would be 1954 Topps. I've built, sold and rebuilt it 3x already.
Basketball is the 1969 Topps set. Loved it since I was a kid. Built it 2x:
Boxing is actually easy for me: H815 Adam Hats premiums
Entertainment, 1976 Topps Star Trek
Football, 1968 Topps. Again, a childhood favorite of mine:
Hockey is 1975 Topps. First set I really built from packs in hockey:
Motorsports, gotta go with the 1976 NASCAR postcard set from STP and Racing Pictorial. Just great looking cards.
Nonsports, I am fond of a series of steamship postcards made in Japan in the interwar period.
Pin-ups, I like a rare set of Cuban tobacco cards from Trinidad y Hnos
Soccer, 1968 Crack from Argentina.