I think it's important to compare funding offers, but there's several things to take into account:
(1) Amount: Can you comfortably live off of your stipend?
(2) Duration: Are students typically funded for four years or six?
(3) Stability: Is continued support guaranteed, or is funding renewed competitively each year?
(4) Work load: Are you working 10 hours a week or 20? Do you get off-years without TA duties?
(5) Nature of work: Will your duties facilitate your professional development or will you be doing tedious grading for 20 hours a week?
logaritym, please keep us updated about the responses you get. Now I am curious