That's such a tough question!
For me I think it's the Namek/Frieza saga.
That whole arc had me glued to my TV. So many twists and turns...and of course the birth of the Super Saiyan
In an age where I didn't have the internet and had no idea when new episodes would actually air. I had to just watch the adverts and hope!
I wasn't the biggest GT fan and have only seen maybe the first two sagas of Super. Is Super worth a shot? I loved the film but hated the Frieza movie and how they messed with power levels, they did my boy Piccolo dirty :(