IR - simulator fidelity
One thing also to consider is the simulator. The fidelity of the AW109 FTD in the UK is poor - no motion and there is a horrible step between the low and forward flight envelopes (although to be fair you are entirely in the forward flight envelope for the IR).
The EC135 is a full motion FTD3 (and an exact match to the aircraft). Having flown both the AW109 and EC135 IFR, there is also no contest - the EC135 handling qualities are far superior. The AW109 has some complex cross coupling effects between collective and roll which are only just suppressed by the AFCS. I don't know what the cost split is though. The job prospects are better for EC135 as you are training with a company that employs co-pilots - it's a 50 hr job interview.
Also remember there is a Single Engine IR on offer in the UK. I now a few co-pilots who have been recently employed on employed on twins having a SE IR.