If you don't currently hold a type rating for either the AS355 or EC135, then you will have to gain a TR on the relevant type before you can undertake the IRT - this should be part of the quote that you obtain from each the training providers (I'm guessing Bristow vs Bond at Stav?). I suppose it would than come down to a decision based on which type rating you think would be the more useful, balanced against your available budget.
E99