The variable rate usually starts lower and its early-exit penalty is three months' interest; the fixed rate offers certainty, but its penalty can be much higher (interest rate differential). Many variable mortgages keep a fixed payment: if the rate rises, more of the payment goes to interest, up to the trigger rate, at which point the lender requires a higher payment.
The choice depends on your risk tolerance, how long you plan to stay in the property and the spread between the two rates at the time. There is no universal answer; there is the answer for your situation.