These days, when engines simply don't come out at the drop of a hat, I would expect the maintenance bills to be cheaper with a 120.
Savoia mentioned a pre-buy inspection - well worth the investment if the engineer knows what he is doing and is given the time to do it. The first Alton Towers helicopter suffered from the latter. Luckily it was basically a good ship.
Back then it cost £80K per year to run.
phil