do it in pattern, so you'll knit 1, purl 1, bring the knit over the purl and off the needle, knit 1, bring the purl over, etc. You do it the same as you do a normal bind off, but instead of knitting every stitch, you knit then purl
I've done both- binding off in seed stitch and binding off in knitting stitch on each of the cuffs on ds's knitted pants. Binding off in knitting doesn't look bad, it adds a little border around the cuff, but binding off in seed stitch blends with the cuff better. I left each cuff different because they didn't look that different from one another (and knitting with variegated yarn helps to hide things like that ).