Your stuff is pretty good and you show a fairly good handling of form and shading. I'm not sure what the portfolio you're assembling is for, but I think you know which pieces are better than others. You must look inside you and pick the ones you feel represent you best.
Sometimes when I have a bunch of average pieces I group them all into one composition which may or may not be greater than the sum of its parts. Kind of like this
The cat drawing is very well done, but I think the fact that it is so clearly based off a photograph takes away from it. I use photograph reference too, because there's no other way around it, but try to reframe the image, or tweak it somehow so it is a little more personalized. Or even better, draw a couple of different sections of photographs on top of each other and see what comes out.
3, 4, 8 and 12 are good stuff. They look like you're comfortable and confident with what you're doing. The rest seem like you're being or trying to be a little too tight.
Replies
Sometimes when I have a bunch of average pieces I group them all into one composition which may or may not be greater than the sum of its parts. Kind of like this
http://www.christies.com/LotFinder/lot_details.aspx?intObjectID=5175617
The cat drawing is very well done, but I think the fact that it is so clearly based off a photograph takes away from it. I use photograph reference too, because there's no other way around it, but try to reframe the image, or tweak it somehow so it is a little more personalized. Or even better, draw a couple of different sections of photographs on top of each other and see what comes out.
Cheers