I dont know if breeding a zwelious to get a deino have a benefit,but if it does,
tell me which choice is better.?I really need it for my team.
A Deino hatched from an Egg would take much longer to raise, as its growth rate is very slow. If you've already caught the Zweilous, there's really no point in breeding a Deino if you can do the job perfectly well with Zweilous. Therefore, I would say don't breed the Zweilous, just catch one and use it.
P.S. The Daycare in Black 2 isn't actually available until postgame.
Hope I helped!