I know there can be loopholes in either. I do feel taxes on what you spend, not what you earn would be easier to enforce and more people would get stuck paying or at least contributing.
Maybe, but that would just rev up the black market. Everything you own would have to have a tax stamp on it.
It would also drive people to save more, which is good, but is also bad for the economy. People have to spend money to keep it going, and if its all sitting in banks collecting interest its not doing anyone any good.
Personally I like the flat income tax better, but either way it should be done with 0 loopholes, 0 exemptions, and 0 credits. Everyone pays the same percentage, no matter if your single, married, have a bazillion kids, or own three homes in three different states.