I want trade with my mobile.
possibly you are going to have a hard time on mobile because some of these platforms are not too mobile friendly.
but herey trade now growth into 0.4 btc .
i can not understand this.
Now , According to the history of exchange yobit.net & poloniex
which out of them you will suggest .
as others have already said, between these two i also suggest poloniex.
try to stay away from yobit because it is shady and there are lots of problems with their service.
and there are a lot more exchange out there you can try.
Because I heard something more complicated like ddos attack , is this true .
DDoS happens for any site, but the safety of exchanges is more serious than that.
they get hacked!
you can search and find it in the history about exchanges that were hacked and ran away like Cryptsy, MtGox, Bter, Bitfinex (this last one was hacked but stayed)
Now between these two which is more secure and handleable for my mobile .
well as i said you will have a hard time and poloniex is a pretty heavy site to load even on computer.
try using a bot or a different kind of service only through their API if you had trouble with any of the websites.