I use iAnnotate and I love it. It costs $9.99 on the Apple iTunes App Store. PDFs that are already OCR'd can be highlighted and whatnot using the software, and searching them is simple. There are also a lot of other helpful tools like highlighting and the ability to add notes (annotate).
The only negative I've found is that sometimes when I zoom in or out and then scroll, the text looks a little fuzzy (like it didn't load/render perfectly). If I change the zoom this is immediately fixed, so this doesn't bug me much, but it is one thing I've noticed. I am using an older iPad so it may just be this.