They all look great, but my favorites are probably the first one, the third one, and the sixth and seventh ones. (Really narrowed it down, didn't I? XP)
I like the first one, and that kinda surprised me. A lot of times that level exaggeration, like on the thin nose, doesn't work for me. But I love how it works here. The long, thin nose, and the tiny mouth and chin pointing out as they are gives of this really great sense of how gravity is pulling his older, sagging face. The direction of how the nose is pulled down reflects the pull on his cheeks. It all works really well to give you this lifelike feel of the character's age. And the closed eyes and closed mouth get opened up a bit by having a kinda dramatic curve to the contour of his face. Somehow. ANYHOO. I like him!
I like the third one, the girl in the hood, because I think she's super cute. Her small little smirk and her eyes make her look adorable.
The sixth one, the girl with the bird, is also adorable. I love the soft, rounded shape of her face, and I like the fuller lips and her round nose. And her eyes! I love how expressive they are as she looks up at the bird. You can really feel her sense of wonder and "what's-going-on-up-there?" as she peers up at the bird. So cute.
The seventh one, the guy with headphones, is great, too. I like how the shaped of his head worked out; his head is kinda taller, particularly from the nose up, and I like how it lets him seem like he's leaning back, cheerily, even though we only see his head. I like his smile, and his overall happy, relaxed look; he has a ton of lifelike personality and energy and I think he looks great.
Awesome ! I'm often trying to do sketches like this, draw random stuff, It's not that easy to start with nothing special on your mind. I don't know if you feel it too (I'm sure you have tons of unfinished and unsatisfying sketches too ) Anyway, great stuff ! Makes me want to pick my styla