Hello Vicke
In choosing a typeface for your dissertation, think first of functional criteria : do you need old-style figures ? small caps ? uncommon diacritics for foreign names ?

The distinction between serif and sans-serif is not that important in terms of readability, in my opinion : you can easily compensate for the lack of serifs by setting a sans-serif with a little extra leading.

Thanks for the reply, Celeste. In terms of the functional criteria, non-lining figures are quite crucial for my content. Small caps and uncommon diacritics are not so important. I'd just a character set covering basic latin glyphs.

That's a good point about the sans serif, in which case do you have any suggestions on ones which work well in long text? I forgot to mention earlier but I am willing to pay for a good font, just so long as it doesn't completely break the bank.

I agree with you about using a serif for body text, for reasons of ease of reading. This is a topic of recurring debate on Typophile, the most recent thread being here.

In my biased opinion, an old style serif gives the most comfortable read.

But you may feel that a more contemporary mood goes with your topic, in which case you might consider Fedra Serif and Sans. The sans in lighter weights to me has a stylish architectural feel, which could work nicely for headings.

Whitney http://www.typography.com/fonts/font_overview.php?productLineID=100026&path=head has a nice architectural feel and is eminently readable (or can be easily made so).