Condoms:
Unconfortable, lower sensation and change the feel totally. The about 99.99% reliability rate thats given for them assumes they have been stored properly, put on properly (for those suggesting the girl does it beware of the nails) you clean up properly afterwards (if theres to be any contact after) and theres nothing that will break them up, a list that includes alot of lubes.
All chemical methods:
Risks some unpleaseant or undesirable side effects. Mood issues and sex drive changes are common. The male ones under development all have the extra issue that theyn arent just replicating an existing block on fertility. The newrer hormone based IUDs hare not immune from the issues other chemical based contros have, the risk is just lessened.
Withdrawl and Rythem:
Both very unreliable, especially if both are over the average fertility and are particuarly compatable (This mostly relates to the female bodies immune response to foreign bodies in it, as one of the many hurdles sperm have to face is the female immune system, a weaker reaction due to compatibilty greatly increases the chances of pregnancy).
Femidons:
Just weird, mostly similar issues to condoms.
Vasectomies: Not 100%, even if the operation apprears to go to plan there are still potential risk of pregnancy. There are also potential side effects, thats before you get to potential mental issues.
Abstinance: Effective as long as adheared to. Tricky to adhear to, but if you do is only method other than condoms and femidoms that actually provides noticible protection against STDs.