Here are my faves from each jjba part* Fave parts are 4, 5, + 7!
*Disclaimer: If Jotaro is in it consider him on the list. He's neat.
Starred characters are overall favourites!

Phantom Blood - Jonathan and Speedwagon

Battle Tendency - Joseph* and Caesar

Stardust Crusaders - Jotaro* and Kakyoin*

Diamond is Unbreakable - Josuke* and Rohan*

Vento Aureo - Bruno*, Mista, Giorno*, and Doppio

Stone Ocean - Anasui, F.F., and Jolyne

Steel Ball Run - Diego*, Hot Pants, and Johnny

Jojolion - Gappy*, Yasuho, and Tsurugi

Ships - Jonaerispeed, Caejoseq, Jotakak,
Bruabba, Gyjo, Dinopants, and Gappyasu!