Consider the following exercises of governmental power.  Which are best left to the states, and which seem more appropriate exercises of federal power?

1.  speed limits on interstate highways
2.  the decision whether or not to recognize gay marriages
3.  hunting regulations for duck and geese (season, limits)
4.  the decision whether or not to allow importation of drugs from Canada
5.  the decision whether or not to allow a particular drug to be sold at all
6.  the decision as to what forms of pornography should be criminalized
7.  limits on damages in medical malpractice cases
8.  limits on emissions from power plants
9.  guarantees of access for the disabled to public buildings
10. the decision of whether to impose the death penalty for murder
11. the decision whether to allow doctor-assisted euthanasia
12. the decision whether to allow abortions
13. the setting of standards that students must achieve to gain a high school diploma

What are the best arguments for leaving substantial power with the states?  What are the best reasons for the exercise of federal power?