The type of reader is strictly your preference - you just need to make sure that it will read the format that YOU create/prefer.
PDF format is pretty common for putting documents on the internet. A lot of people on this forum talk about converting everything to PDF with searchable text layered underneath. That way you can see what the actual book looked like (from the picture) and if you want to search for specific text it can do that too. If there are any OCR errors, I don't think you would actually see them, they just wouldn't respond correctly to the search. Some people - mostly students with textbooks or people doing research, or people digitizing historical documents - want to keep the exact layout as the book/document they are scanning - it is important to have page numbers for references. PDF's do not take advantage of one primary function of ebooks - the ability to "reflow" the text to fit the size or orientation of your screen. I don't know how often I've been frustrated trying to read technical manuals that have multiple columns in pdf format. I would have to scroll horizontally and vertically multiple times per page. On a desktop display it's not as big a deal, but if you get into smaller displays like a tablet or smart phone that would be crazy. To see the whole page at one time - the letters would have to be so small that my old eyes wouldn't see them!
I personally prefer to do the full OCR and store the file as text/html. This usually results in a much smaller file size - that way I can fit as many books on my reader as possible. Also, most readers can handle those formats. I say MOST but you need to make sure that the reader isn't limited to a specific proprietary format. Rocket books, original kindle, etc wouldn't read anything but their own format. If the reader can't handle text/html it is pretty easy (there is usually free software readily available) to convert from text/html to whatever format you want. The down side is that it takes a bit longer to do the full OCR and then go back and check for errors. The good thing is that if you set up your cameras properly and get a good scan to begin with, the software we use here, scan tailor or book scan wizard, fixes most common scan errors making the OCR much more accurate.
A particular format that is pretty much becoming the "standard" format for ebooks is .ePub. It is basically just .html, image, font, table of contents, and style files (plus the new ePub 3.0 will allow audio and read-out-loud files) all packed into a .zip file. Then they rename the extension to .ePub. If anyone cares to rumage around just rename the extension to .zip and you can open it up. The benefits of this format are primarily that "most" newer readers will open them. But even better, there are a few FREE software programs out there that will automatically create, or reformat, the ePub for you - http://calibre-ebook.com
comes to mind, but there are others. If you want to see how it can be done manually - or just want to spend a few minutes because you have nothing else to do - check out a tutorial that Aaron DeMott put together over on http://www.jedisaber.com/ebooks/formatsource.asp
One reader software (works on windows, iThings, windows 7 mobile, and android, with OSX still in the works) that seems to do a good job with display of pictures, formatting, readability, etc. is "Blio" http://www.blio.com/
. It reads the ePub and XPS(??) format. I have only looked at it briefly so please don't take it as an endorsement.
I know that is a lot of info - but the point was that any "reader" you get needs to read the format that YOU create/have. After that it's just your preference on what bells and whistles the reader supports to make your job - reading the book - more enjoyable.