I voted both because it really does depend on the jersey for me. I have a few that have elastic and I like them that way...and a few that don't. I've taken the elastic out of two shirts because it annoyed me.

Now that I think about it, I guess I like the elastic on shorter jerseys. On jerseys that are longer than my hips, it drives me nuts because the band rides up and the fabric bags around my waist. When the shirt is shorter than my hips (which actually happens pretty often as I have a long torso), I like the elastic for keeping things 'modest' when I am bent over on the bike.