Of the 4 you have on your site, Alexander is the best. The style you drew it in is simple and the lines are nice. It has a good flow to it. The others, it seems as though you attempted to be more realistic and have added more shading to try to achieve this. I must say that the other two sketches need a lot of work, if realism is what you are trying to accomplish. They are very rough and the shading is choppy. You need to work on shading with a lighter hand and try to blend the tones better. realism takes a lot of practice. So do not be discouraged. I am sure you will improve with each drawing.
all the best,