Need some help.

Well I started the game with a shitty team and only after than I came to read a few things and I decided to restart and go for the rerolls.
Which captains should I aim for?
I did around 50tries still no shanks and no ace.

btw 50tries= 100 rolls

So best possible Captains you would try for would be dependent on whether you feel it is worth rolling for one you can farm, but the following would be usually ones people were rolling:

Farmable:
Arlong
Vivi (Though not yet, will possibly need to wait another 2-3 weeks until Laboon Island comes out where you can farm for her base Miss Wednesday)

Not farmable:
Ace
Shanks

Not farmable Crew Members
Nico Robin/Miss All Sunday

Obviously if you end up not rolling one of those in 3 days, then you should also consider aiming for Balloon/Gear 3rd Luffy, Wolf Flow/Lion Stance Zoro, Fine Tempo/Happiness Punch Nami as great captains