I have flown both and from a piots point of view I liked the MD902, lots of power and not too sensitive to wind direction.
From an operator's point of view though I would go for the 135 as it will probably have better support from Eurocopter (at least in Europe) Residual values should be better as well. I really hope the 902 does well as it is a great idea but it is going to be a brave commercial operator who buys a fleet of them.
I also flew the EC 155 recently and it is an impressive machine from a pilots viewpoint. It should give the 76C+ some stiff competition but it needs a higher TOGW to really compete in the offshore market.