Change in emphasis in the initial IR
Just to add another facet to this discussion, the CAA has recently agreed a change to how initial helicopter IRs can be conducted.
With increasing automation, the CAA have said that use of autopilot upper modes (eg IAS hold, HDG hold) will be allowed for more of the test profile. In fact the only manual requirements will be the initial climb to altitude and the 3D approach. Whilst purists are going to decry the potential to lose (or never acquire) hand flying skills, let there be no doubt that the IR is still a huge hurdle to cross and hand flying will still feature heavily in the training.
With that in mind, I'd definitely look at which aircraft had the best autopilot! And which training provider had the best simulation of that autopilot. The AW109 and EC135 probably have the most comprehensive suites of AP modes with the EC135 probably just nibbling the AW109 in terms of features (eg better protections, fly-through mode, better heading control (can do >180 turn without reversing turn)). I can't comment on the twin squirrel AP but I suspect it's not as powerful. The mighty Longranger probably doesn't need the AP!
The Helionix AP on H145/H135 would make the IR a doddle (relatively). If you had a big bucket of cash, I'd consider those. But you can dream...