Choosing an offer is not an easy task to do.
This file talks about our experiences in choosing 
and PhD offer out of several
received responses. The easiest choice is if you only get one offer.
Another easy choice is if you get one offer from a very competitive
university (5-10 ranks higher) and the rest of them are low ones.

If you still have many offers and this is the main case and you don't fit
into the above described patterns, you'll have to decide. I personally
would go for the highest rank, assumed the university maintained that rank
for some time already, having some history. But there are also others
who will choose different.

This is a personal issue in the end. I'll just point out things valid 
for ANY (or most ;) individual(s) who seek(s) an academic career.

1. The main ideea is here not to be fooled by big money. Money 
   should NOT be an issue, assuming that you want to finish your PhD.
   Don't compare offers by offered money. So many things vary from 
   state to state, from university to university !

2. Statistical factors such as crime rate & etc. should also NOT be
   an issue, assuming you'll study most of the time.

3. Weather, location and campus environment MAY be considered being important
   things to care about.  Working in an unpleasant environment is not giving
   the same results.

4. If you're granted an TA or RA (meaning money ;) you should also consider
   things like: office location, does it have windows, do i have to study
   more just to be able to teach or will i be able to do it easily. etc.

5. Summer Vacation related issues are also important. If you are awarded
   money you should not dispere if they don't provide for the summer. You might
   be able to get some internship and to work for more money.

6. Do they consider your previous graduate study (if any) for maybe waiving
   some required coursework ? If yes, this might save you a whole semester !

7. Besides the professor you want to work with, are there also other persons
   you might be able to rely on, in case you just don't fit into his team ?

8. etc.