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 think to become a good trader reading doesn't help a lot. What helps is experiencing it first hand and making mistakes because mistakes are painful and teach you not to repeat them. One thing that is good to start with is to not start with to much and that is what you seem to be doing. Reading adds to your knowledge, but experiencing it is different.
Regarding manipulation @Neuroticfish, that is probably the same for both BTC and BCH.
Who really knows what's going on between the Bitcoin billionaires?