what you need to learn how to do is to read up on how to use pen tool
with pen tool you can precisely mark out your char and cut him out and then place HIM without the background of the original picture you found him in
what's wrong with yours 1st pic is precisely that, you need to cut out the ugly black background and leave only the character itself
the second one is ok, but would be better if you find some cute char for it

, I think the second one is your best one
and the 3rd one is the same as the 1st one, you didn't cut out your char and you left red and white background with a black and white backrgound left with the char.....