I chose the Sontarans, as I think they do a good job of matching the "nasty, brutish and short" description given by the Third Doctor. The make-up they use on the head is very good, and I like that the body armor looks more like something a warrior would wear as opposed to a sparkly jumpsuit. After "The Time Warrior", I was never a fan of the Sontarans costumes they used, I felt they declined in quality, and I was never sold on the shape and size of those heads on those tall bodies.
As for other monsters...
I think the Daleks have done a good job too, the bronze ones look like good tanks, and I'll even admit to liking the shape of the Paradigm Daleks for officer classes. I will say that they took a big mistep in terms of colors though; instead of being multiple bright plastic colors, they should have made them more uniform and metallic, the red Drones in "Asylum" looked good and could have easily done for the new default Dalek drone. I do feel worried however that because of the negative reaction to the Paradigm designs that they'll never give them a redesign again, which I don't want, since I want them to keep things fresh and mix things up every once and a while. Otherwise I know I'll grow tired of the bronze ones sooner or later.
The Cybermen have done mostly well here. I like that they've gone a more machine-like route, further separating them from their humanity, with the "Nightmare in Silver" being my favorite one so far. I will say that the Cybus one is a bit too much in places, with the loud stomping and the nonsensical DELETE.
I appreciate that Silurians have been given a more human-like design. The Ice Warrior shell looks like real armor and they got rid of that hair. The transformation for the Zygons was excellent and they were more understandable.
Generally, I think New Who has done a fairly good job with redesigning Classic Monsters. One of the reasons I want to see so many monsters return to the show is just to see what they would look like today.