The problem with PDFs is you are trying to read them on that tiny screen. The only e-ink devices that do a good job with PDF is the $1000
Sony DPT-S1, the Kindle DX, and similar large-screen devices of which there are few.
The browser is always going to be terrible, partly because the average ereader does not have enough RAM, partly because the screen again -- with a refresh rate that can be sensed with the naked human eye, that will not be a pleasant experience. And screen size, again.
Although it is more usable when browsing with this hack:
SkipStone browser for Kindle Touch
That should suffice for predominantly text-based websites, in fact I actually browse MobileRead using this, in a pinch.
Any ereader can read any format, if you use
calibre.