Since nobody here has said it yet, you got three choices:
The cheap orange box sets - $20-35 each. It has nine seasons. It was cropped into widescreen and digitally remastered with questionable results.
The Dragon Box Sets - $25-50 each. I haven't bought these, but they are still releasing a new set every other month with more episodes. Is in the original 4:3 format. Remastered properly.
If you hated all of the filler in DBZ, but still want to buy it, then...
Dragon Ball Z Kai (Blu or DVD) $20-40 each. Are only released in half season sets though. Series has been upscaled to HD and remastered, and edited to only follow the manga. That means no Garlic Jr, filler episodes, no long drawn out battles, etc.