I typically pick up DST's on a week to week basis depending on their opponent. Right now I have a waiver claim in for the 49ers (yeah I know, some dummy in my league dropped them), but I doubt i'll get them seeing that I'm 9th in the waiver claim order. So here are the choices, not really any great options, but some potentially good ones:
Cowboys vs TB
Dolphins vs NYJ
Colts vs JAC
Broncos vs HOU
Of those 4, the Cowboys and Broncos probably have the best defenses, but they are also playing good offensive teams. Tempted to play Colts DST just because Jacksonville is so bad on offense, but I could still see the Colts giving up 21+ points to Blaine Gabbert. Think I'm leaning towards going with the Cowboys, big redemption game for Rob Ryan after getting embarassed by the Seahawks.