Thud's "I've-got-an-opinion-on-everything" perspective:
I flew the 902 for 2 years, and now operate the 135. Pilot points can be summed up as follows:
902 has good cockpit layout, with no roof-panel switches and logical positioning for just about everything. Good, simple FADEC and manual engine control. Rotor brake works, and can be used without fear of bits coming off. As my instructor was wont to say, "the pilot was definitely in the office when the 902 cockpit was being designed" - Eurocopter probably sent theirs on leave. Large cabin with ample headroom & good access.
902 yaw control is not as good as the 135; easy to reach torque limits with pedal input, and downwind hover/ backwards orbit are often a handful. AFCS/ AP can be a hindrance in police work, but lovely for point-to-point stuff. Only one AHRS, a subject the UK CAA get very excited about for single pilot IFR. I can see their point - obviously I'm not going to notice deviations from my intended flight path as I sit there reading the newspaper or eating my breakfast during an IFR transit
Not qualified to talk from an engineers perspective (there are some in the company who'd query my ability to talk from a pilot's, come to think of it...). The 135 is definitely more solidly-built; cockpit windows and doors tend to stay in their intended position (ie on the aircraft) with the Eurocopter offering. Access is definitely better on the 135 - the 902's flimsy panels all have to be removed to work on the engine, and those Camlock fasteners on the 902 often used to give me opportunity to practice my Anglo-Saxon.
Despite Eurocopters claims, I can vouch that the 902 is the quieter of the 2 aircraft when they're operating overhead. Neither is as loud as tail-rotor aircraft though.
Overall? I'd love to go back to the 902 from a pilot's point of view, but the spares/MDHI situation sounds as if it's reached PNR.