It depends on the heli and setup I think, I have a Titan with an OS 50 Hyper engine in it and it has given me no problems at all. I love it as it is powerful, stable and aerobatic all at the same time.
I also have an old Nexus 46 that I bought second hand and it has not been so easy going, there is a pin in the starting shaft that shears quite often that puts an end to your days flying before you even leave the ground.
In ballance to the above I just got a Trex450s and put the 3rd and 4th flights on it today, I love it already. Clean, powerful and aerobatic, not as stable as the Titan, but I expect if you get an electric heli the same size as the Titan it will be stable as well.
As stated above, I take both the Titan and the Trex to the field, so I can fly the Titan while the Trex charges. I intend to use the trex to learn new moves that I can do on the sim before I risk the Titan as it costs over 3 time the price.
So if you have good kit that dosen't give you hassle, both power plants are 'worth' it, IMHO. [8D]