Which of the four Dragon Ball series is your favorite?
OG Dragon Ball.
In my opinion, OG Dragon Ball explored the adventure-type nature of the series the best, which is ironic because it was exclusively focused on the Earth whereas the following ones all went to the stars, if not even other timelines or universes. It was a genuinely fun journey to go through alongside Goku and co., watching each story unravel until a climactic battle, which was the general formula for the entirety of it, with an occasional tournament arc here and there. Not only that though, but the original fights in Dragon Ball clearly had more thought put into them, as many of the fights focused on planning, techniques, and were generally very grounded with few Ki blast's as special attacks. It was a polar opposite of the more modern style fights adopted mid-Z and after, which focus heavily on the sheer power being displayed, who's simply outright stronger than who, and Ki blast's are used about as much as HTH combat. While DBZ had some good moments with characters using strategy, it was just never on the same level or as consistent, whereas DBS only pretends to bring that back in the ToP arc then never actually does anything cool with it. While I do like both styles of combat, I prefer the OG way a lot more.
DBZ does have better aspects though, I would say. For example, DBZ adopts a much more serious and dark done than OG Dragon Ball, excluding maybe the King Piccolo Saga. In DBZ, Toriyama puts a heavy focus on how high the odds seem to be stacked against the heroes, but shows an impeccable fight that ends with the heroes being victorious, despite heavy losses, and does it in a way that feels realistic (usually). There is a REASON why Dragon Ball Z is used as the focus of a lot of inspirational videos and music, because it is inspirational. Goku is inspirational, he has a lot of the core elements of a classic underdog story. In almost every major fight he's in back in DBZ, he's nearly always on the losing end, but through a mix of strategy, technique, and most importantly, sheer determination, he manages to overcome each threat every time. OG Dragon Ball only REALLY had this with King Piccolo, and even then it didn't feel as one-sided against Goku because Goku was outright stronger in their second fight.
OG Dragon Ball takes a more laid-back tone and pace, a simple, entertaining trip through the mystical and compelling story of Goku and his friends, with some hiccups along the way, and some amazing fights. DBZ takes a more serious, high-pace, action-centered tone and pace, focusing on the trials Goku and his friends must overcome to protect the Earth and/or the ones they love, somehow overcoming nigh-impossible odds at every turn against unimaginable foes. Both are great on their own, it really depends on just what kind of story you prefer more.
Then you have GT and Super.