300CBi
While it is not mandatory to learn to fly on a piston engined machine, it is effectively mandatory for many - cost being the limiting factor.
Anyone with the funds available to train all the way to CPL in an EC135 would be looking at a different machine for ab initio training and then an IR after the CPL.
Before you completely rule out piston-engined training perhaps you could consider the Schweizer 300CBi. This machine is very stable, capable of full down autos and (relatively speaking) widely accessible. It is one of the more popular training machines worldwide and a damn sight cheaper to run than EC135!
Good luck and enjoy your training.