Each has its ups and downs. The Bell vs Eurocopter thing has been going on for years like Ford vs. Chevy, and we may as well be arguing about our favorite colour. One could tit for tat for hours on end.
Dynamic, you'd be well advised to pay attention to 407 Driver. He is among the finest of helicopter pilots anywhere, and has reached a level of knowledge and experience in the Canadian Rockies that most of us can't even imagine. As you may have noticed, he doesn't talk through his hat, and can back up his words.
I can only speak from my own experience, which is operating 350s commercially for 1500 hours, and flight test on 407s for about 1000. I don't work for Bell anymore, and have no particular allegience to them or anyone else. I can tell you that I know the 407s problems intimately, but would not hesitate to operate one anywhere. It is a superb helicopter.
We have just over 200 AS 350s operating in Canada. They have had their share of growing pains, like anything else. The Turbomeca engine, once the savior of the type, is quickly falling out of favour due to reliability issues and horrid product support (Widgeon, a quick call to Irving in NB who operate a 350B1, L4 and 407 will enlighten you). In fact a 355F1, with two Allison engines has a lower operating cost than a 350B with one Arriel. You are correct that Conklin and DeDecker do indeed list the 407 DOC at $36 more than a B2, but I think the servicability issues and performance more than make up for it.
The hydraulic failures persist, in spite of being identified eons ago as a problem. In the past 8 years in canada we have had 9 reported hydraulic failures in Canada. Some of the belts had 200 hours.
In the same time, there have been 15 forced landings due to inflight power issues. Admittedly, it's likely that not all have been directly engine related, but that's still one out of every 13 helicopters in 8 years of data (assuming there were 200 A-Stars 8 years ago - and there was nowhere near that). Of the 25 407s in Canada, there have been two engine power incidents, one is still under investigation as to cause. There have also been 520+ production models and several thousand hours of experimental which have been built at Mirabel without a failure in flight test. Touch wood.
There have been several accidents involving main rotor spherical bearing failures. Very serious problem.
My biggest worry about them is the survivability in an accident. Lawn furniture surrounded by ping-pong ball skin. Give me that box structure of the 407 anyday. It's even stronger than the L with the added composite. Another misconception is that the 407 is an L4 with 4 blades. In fact, there is only 14% commonality between the two ships, and one cannot build a 407 out of a 206L-4.
End Rant.