iBooks doesn't support scrolling of PDFs, also in landscape mode it just zooms out whole page to fit on screen which is kinda silly.
GoodReader also doesn't support proper PDF scrolling. I don't uderstand how people can call it an excellent reader when it doesn't let you scroll through PDF pages like you do on your computer or on Apple's own internal iOS PDF viewer.
Adobe Reader lets you scroll PDFs, but it also displays same page number popup which cannot be disabled, and a little bit slower than iOS viewer.
There is no perfect PDF reader for iOS.