skydsl as isp, dns server question

Hello,

I am with skydsl since many years now.
But the speed has been going down more and more.
Sometimes I even cant get conncted to the dns server which is recomended for skydsl.
Is there somebody who kows more about the dns servers of skydsl or which dns servers are recommended.
Is skydsl still the right adress as ISP ?

Regards Andreas Nielsen