As for difficulty:
Worst is ICP- ME
Many of the wet chemical methods can only detect heavy metals as lead. They usually detect this as the sulfide and produce a dark or black color. These often use hydrogen sulfide and can be dangerous. Other color methods are out there, though.
To give you an idea of what you are dealing with, let's look at flame AA. It takes the solution you are analyzing, mixed it with acetylene and air, and sends the mixture through a lot torch. The torch has a beam of light bedding through it from a hollow cathode lamp.
The air and acetylene is mixed before the flame, so if anything should happen to cause flashback, you get a big bang ( and other bad effects). Now imagine if you are analyzing gasoline for any lead. Sometimes the results were very nasty.