The full size iPad is my go-to ebook reader (for epub documents) as I like the 4:3 screen ratio as opposed to most android tablets which have 16:9 dimensions. iBook reader is, to me, a so so reader because (1) the book title appears in every page, and it can distracting if it is a long one; (2) there are no options to change line spacing or margin widths; and (3) the fonts are limited to six, none of which I particularly like. My favourite reader is Bluefire (or any reader using the Bluefire engine) as it addresses the failings above.
Also, font-wise, you have the choices of any of iOS system fonts. In addition, since IOS 7, you can install additional fonts (without jailbreaking your iPad). To do this, go to http://www.fontsquirrel.com/, choose a font to your liking, and click the “Install On IPAD” button. The installation will create a new iOS profile for your iPAD, and the new font is now available as a system font.
I used to like EB Garamond font, but now my default font is Linden Hill. Here is a screenshot of my Bluefire ebook: nice, lots of white margins which I like, Linden Hill, no distracting book title, and I can control the line spacing:
Earlier I mentioned about installing additional fonts for your iPad through http://www.fontsquirrel.com (especially to use for your ebook reader). The shortcoming of this is you are limited to the fonts listed in the website. No worries, now you can install iOS Font Maker (free!) on your Mac or PC, and you can install any TrueType font you can find on the Net on your iPad or iPhone.