I've tried Adobe PDF reader, EzPDF and RepliGo. My impressions are:
- Adobe PDF Reader - Worked OK and is free, but it's slow.
- EzPDF - Works OK, but is just a little bit faster than Adobe.
- RepliGo - By far the best one. Faster and more responsive. When you are zooming and/or panning, it uses a low-res pre-render so you can quickly center the screen at the exact point you want before it completes the rendering.
If you just want to view some PDF files from time to time, Adobe works ok, but if you often need to view large PDF's, specially with images, I strongly recommend RepliGo.
By the way, it's not US$8 anymore. I think it's 3 and something.