Kryptonite w/o a doubt IMHO.
They come in 3 foot and 5 foot lengths, even 5 feet is too little to go around a post and some part of the bike easily.
I recommend getting a pair, 2 5 foot chains and 2 locks, that way I can use one lock on the end of the chain to make it a lasso around a post, then it gives me 3 feet of reach with the free end, the second lock and chain actually secure the bike to the first set.
Too much to carry.
I got 4 sets of the 5 foot chain w/lock to leave one at work chained to a post, the other at home.
Nobody's gonna steal the one I leave in place at work.
I paid about $99 for each chain + lock setup.