It also depends on, you know, your hygiene, mang. Wash your damn hands.
But more than that, it depends on your unique body chemistry. I'm not going to pretend to understand the nuances of pH levels/diet/persperation, but I can tell you this: I kill nickel strings within weeks. I kill (quality) steel strings within months. A good set of DR's will last me six months before they start to fade.
Additionally, I used to be heavily pierced. All my jewelry was at least 316LVM surgical stainless steel, internally threaded. The one time I wore sterling silver (which contained nickel - it was a gift) my lip swelled up to twice its normal size, and I was in constant pain.
You can get into all kinds of arguments about your pick angle/attack. Tolex, rubber, nylon, graphite, what have you. Unless you're a serious punk rocker, or playing with a metallic pick, I don't see any impact upon the life of your strings. From your right hand, that is.
Your left hand will most always be in contact with your strings, and that's what you need to worry about. That's where you're going to be rubbing your acidic man-juices onto. A standard pick will move your strings with slightly more energy, and - depending on technique - impart that energy in a way that rubs against the windings in a generally negative way. Any attack straying from a parallel angle to the strings will, theoretically, create minor (minor [minor]) gaps between the windings. If you touch your string in the exact right spot where it's separating, or - heaven forbid - the string starts to unwind over a crucial point, such as the nut or bridge, you're boned.
I wish I could be more help, but... I am drunk. My ultimate advice is, as always; try it out. Nobody knows better than you.