what would you say is the best way to get z-points fast

I would say... Tournaments. Actually no I would say Ultimate battle Z!

I got all the zennie by geting the dragonballs and wishing on red shenrong for 50000 zennies I did it until I got enought to buy everything and unlock all the characters slot.

Mission 100. You get a shit load of Z Poiints in a short amount of time. I was able to make 100,000 Z points in about a one hour time priod.

i dont think mission 100 is a good way :/ cause you have to fight more opponents and get as much z-points as for defeating one opponent. i think disk fusion with bt1 is a better way to do it. take burter and do some high hit combos, loose as little health as possible and you'll be rewarded with about 2,5k-3k z-points per battle.
best way is still searching the dbs