4. The Sontarans - The Sontaran Stratagem/The Poison Sky
I'm just going to come out and say it. The Sontarans--on their own and without context--look kinda silly. Not quite Abzorbaloff silly, but they're not the most physically imposing of villains. But as we learned quickly in "The Sontaran Stratagem" and "The Poison Sky," the Sontarans are more than formidable. The massacre of British soldiers--unprepared and equipped only with inadequate armor and inadequate weaponry being shot down by the merciless Sontarans--made us all feel at least a little bit guilty that we laughed at them for looking like potatoes. Now, however, with the introduction of Strax as a friend to the Doctor and a comical figure to the viewers, the Sontarans seem so much less threatening. His interactions with Rory in "A Good Man Goes To War" were poignant and touching, but his transition from warrior/nurse to Victorian butler both lessens the circumstances of his original death and reduces the fearsome reputation of the mighty Sontarans. Strax may still want to blast the crap out of everything and he definitely works as the lovable comic relief that is sometimes very much needed on this show, but a Sontaran invasion should probably be delayed until a time when they can be properly scary again.