Railing's your best bet, if you do enough it'll kick in pretty quick, and last a while.
I'm sure someone will throw up some BA percentages, but imo up the nose is the way it goes when it comes to Xanax.
Xanax for me was a bit weird, I was on it for a few months and didn't realise it was doing much after the inital dose....Well it was but I didn't feel it if you know what I mean. I would stare off for a while, and think yeah this is nice, then just like that it's gone....
That said, some peeps love the stuff, enjoy