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.
I am with NeuroticFish on this. The only thing I would add is that the way you are asking you might wanna go to the casino and try you luck there. The mathematical expectancy is negative over the long-term but if you win you'll make your money faster.
If at some point in the future you consider a long term vision for investment, besides having understood what is the Bitcoin and shitcoin cash, maybe an interesting option is to buy $250 of Bitcoin and not sell them, but keep buying every month what you can $250 or $50 until with what you buy and the return you accumulate a good capital.