ehhh....it looks like you're going on a good track, but you're still not quite there yet.
the first and second look unfinished to me...like the stock was cut out wrong and there's no background. random lines stick out. the third one with the "K" doesn't help it look better.
the fourth is my favorite out them all. it looks like a good stock and it looks like you had good direction but all the extra stuff besides the robot just looks a little too dark. i almost feels like there's a little too many layers too. the lines over the robot are really distracting.
the fifth/last just seems like random effects added to the background and over the stock. theres just nothing about it that makes it stand out to me.