What should I buy?any advice?
Neither. If you are asking this then you have no idea what you're doing and you don't know the differences (at least as investment) between the two coins.
Learn more and then you'll know what to do. A 250$ investment is not that time critical.
will bitcoin cash increase 50% more from its price today? or I just go to bitcoin cause it's more safe?
Do you expect us to have a crystal globe and predict the future?
Neither is really safe, it just .. one is altcoin, hence in theory even more volatile than Bitcoin; also it can be the subject of heavy price manipulation. And the other one is Bitcoin, which, now it goes downside although it's expected to be in the middle of bull run.
As I said, you have to read more and decide for yourself.