1. Androids arc - For me, there's no contest; this is without a doubt the best arc. Trunks is interesting, the constant twists, Goku's farewell... Even Z's filler in this arc was really good! (Yes, this includes both the cars one and the Tao ones)
2. 21st Budokai arc - Probably an unusual choice for second place, but this arc, including the training mini-arc at the beginning, is so fun. Every time I watch Dragon Ball, the thing that gets me through the less good episodes from the Pilaf arc is the thought that this is up next. Every single time I watch this, I have an absolute blast. It's silly, it's over-the-top, and it's great. I love every moment of it.
3. Piccolo Daimao arc - The turning point when Dragon Ball began to turn into the style it would adopt for all of Z. Although unlike Z, this keeps a lot of the martial arts stuff that was largely dropped in Z in favour of energy attacks and transformations. The first major character death(Which gives me chills every time), my favourite Dragon Ball villain, everything about the Mafuba and Roshi's backstory that this arc goes into, it's all great.
4. 23rd Budokai arc - I really love my tournament arcs. This one also has the really cool stuff about Piccolo, and the ending is brilliant. Also, unlike many people, I enjoy the end of DB filler.
5. Freeza arc - Another major turning point in Dragon Ball history. Freeza is a great villain, Vegeta is awesome as usual, and begins the greatest character arc in all of Dragon Ball. The Super Saiyan transformation is unveiled, and there's even comedy for the dub fans
PelicanDynasty -- I'm right there with you!
And here's a brief look at the other arcs, in case anyone cares...
6. 22nd Budokai arc - Another great tournament arc. Also, it has the Man-Wolf joke, which I love so much.
7. Boo arc - I like it. It was definitely flawed, but I still enjoyed it.
8. Pilaf arc - A humble, and very enjoyable, beginning.
9. Saiyan arc - Goku has a son? Goku has a brother?! Goku is an ALIEN?! Goku teams up with PICCOLO?! Goku DIES?!?! WHAT IS GOING ON?!
10. The Red Ribbon arc - This arc is far too long to do justice in such a small space, but suffice it to say, it's good, although, a little draggy in places.
11. Goku Black arc - This one still needs some time to sit with me to be honest, but for now, I'll just say I enjoyed it.
12. Champa arc - Another fun tournament arc. I liked it.
13. BOG arc - Beerus and Whis absolutely steal the show, and it actually kept continuity with GT, which I liked.
14. Shadow Dragons arc - Amazing premise, slow start, incredible ending. Overall a fun experience, if a little mixed in places.
15. Baby arc - Another mixed but fun overall experience.
16. Super 17 arc - It's fanservice. The premise is thin, it's a little stupid, but it's fun.
17. ROF arc - It had its moments, but it was a little dull overall.
18. Black Star Dragon Ball arc - It's okay. I appreciate what it's trying to do, but it doesn't quite get there really.
19. Potaufeu -
The point of Dragon Ball is to enjoy it. Never lose sight of that.