Originally I was opting for 64GB, but I'm a tad short on money, so whilst I can afford it, if I don't need it, then I could save £100, on the other hand I don't want to be caught short and fill it up and then regret not spending more as I do want it for at lease 3/ 4 years.
I have an iPhone 4 16gb which i bought around launch time. I always regretted getting the 16gb when i found myself gradually filling up the phone with apps/games.
However, i bought the 32gb in the iPad 3 and now its used mainly as my gaming device which i prefer, so i opted for the 16gb again in the iPhone 5 as i doubt i'll use it as much for major gaming as i did with my iPhone 4.
Since owning the iPad 3 Ive actually regained space on my ip4 because i dont install games on it anymore.
So basically if i didnt have the 32gb iPad 3, i would get larger than 16gb storage for iPhone5... Got there in the end lol