...it would be the power of invisibility.
I've thought long and hard on this (doesn't everyone?) and this is the best answer for me.
Being able to disappear from view at a whim would suit me just fine. Perfect for all of those times when I see people out and about and I just don't feel like talking, easy solution, just disappear! I'd even be happy with an invisibility cape Harry Potter style - something lightweight and small enough to fit in my handbag. Even better if it was crinkle-proof.
I had looked at the power of flight - being able to escape into the sky superman style would be a wonderful release but then I realised that I don't look good in tights and like I learnt on The Incredibles, capes get caught and will drag you to your gruesome death. Likewise the realisation that things that fly get shot at. So no powers-of-flight for me.
I also liked the idea of being able to read minds but when I looked at the freaks around me (and there are a lot of them, lets be truthful!) I realised that the less I knew about what went on in their freaky heads the better!
Speed was another superpower up for consideration. Being able to race around and finish chores faster than the speed of light would leave so much more time to enjoy the finer things in life (you know, reading, red wine, chocolate) but when I thought about it, it would actually mean more time to do more chores, all those ones that get put off because I don't have time to do them now. So no on that one too.
Being able to breathe underwater would be cool but considering I don't put my face underwater as it is, it would be wasted. Likewise being able to produce flames/ice/storms etc at will - I just wouldn't have the use for it. And as for a skeleton of adamantium a-la Wolverine (don't tell me you don't know what it is! Hugh Jackman in a chesty bonds...ggrrrrr!), well, I'm a wimp and I don't have it in me to go through the necessary process to get one. I don't care that much.
And as for super-strength.....well, I don't care to be too muscle-y. I mean, I'm all for strength and toning but biceps-of-steel look odd on a woman. And I like having a neck.
So invisibility it is. There you see me, there you don.....