Are Grad PLUS Loans Generally Better To Choose Than Private Loans? Should I Be Concerned With A Variable Rate Over A Higher Fixed Interest Rate?

I'm attending law school in two weeks and need to narrow down loan types. I've already applied and been approved for Stafford loans, however, I need to apply for additional funding to cover the remaining expenses (nearly $40K worth). Distinguishing factors between federal aid (Grad PLUS) and a private loan, are the 1) fixed rate vs. Variable rate option, 2) loan repayment/deferment and consolidation options. Generally though, which would you recommend?