I'm a third of the way through DB, going to watch all of DBZ as well.
GT though...I have it all, donated from a friend years ago. I've never watched it all in order, heck I've barely seen any of its awful first half or so.
It tries to be DB so hard in the beginning and fails so spectacularly. Then it tries to be DBZ and fails until it gets better villains near the end.
The "Lost Episodes" is actually decent in its own right, but fails as a sequel to DBZ. DBZ already established that the characters were overpowered, so it never really feels like the heroes are in any sort of danger.
The Baby Arc is actually decent, the ending with Piccolo saying goodbye to Gohan is actually pretty damn emotional.
The Super 17 is basically a Greatest Hits of DBZ with them battling Frieza, Cell, & Android 17 again. But its cool that #18 was given a story role, and its only 6 episodes.
The Shadow Dragons has a neat concept, but most of it is just battle after battle after battle. Granted, DB and DBZ were like that at times too, but GT battles are more Ki-Spam oriented than DBZ was! But Vegeta gets some decent development here, and the ending is great.
Oh, and the TV Special is actually pretty good too.