Charlie Stross posted twice recently on the subject of three wishes. The first was a simple "You get three wishes!" and the second was "You get three wishes but your worst enemy gets double what you wish for!" Of course the second one isn't very interesting - the classic answer is to wish to lose one eye, but wishing to lose one kidney, wishing for half of a nuclear weapon which will detonate in 10 seconds or other such notions are the same, if funny.
I don't find it very interesting to sit around trying to determine who can come up with the most legalistically bulletproof Happiness For All wish wording so I tend to restrict myself to wishes that just work on me. Without that distinction I think people generally end up spending all their time wishing for happiness for all (as defined by each individual) and then wishing for nobody else to get any wishes to prevent some jackass from later ruining everything by wishing for a gajillion dollars and for everybody else to be 1 centimeter tall. This also hopefully means that the genie/god/witch granting my wishes won't get all bitter on my ass and destroy my life since they tend to have issues with people trying to do too much.
1. I wish to be able to prevent or repair any harm or degradation that may occur to my body, memory or mind at will.
Sort of like invulnerability, except I can allow myself to die or be hurt if I want to.
2. I wish to have the ability to teleport myself safely and comfortably at 99% of the speed of light to any location I can clearly identify.
Best to not risk violating causality, hence the 99% restriction. Unfortunately this means visiting other star systems isn't feasible. I could take a jaunt out to Mars though.
3. I wish to be completely unaffected by wishes made by other people.
This seems prudent since apparently I live in a world where wishes exist. I want to avoid preventing other people's wishes entirely but I don't want to get ganked by them.
If my worst enemy got these powers I wouldn't actually be overly concerned. Mostly the people I hate the most are people who are powerful socially in terms money or influence and I while I wouldn't especially want them to become more powerful I am not sure this would even change that overly much.