Dude, your situation sucks. I'm in the situation where my parents favor my sister too. I don't "try" hard enough and get crap grades. I have the potential and know it, but everytime I do something right or get a good grade, its never enough. I try and show the rents I do as much as I can, but in the end I could have done more. For example, I'll mow the front lawn when I'm asked, my dad will come home and question why I didn't mow the back too. And this is after I've done the dishes, washed my car, and cleaned my room while my sister is still asleep until 1 in the afternoon (I was never allowed to sleep past 10am growing up). I don't get allowance, it is just expected of me. I just got a job (at a very difficult store to get a job at). Still doing all the same stuff everyday and getting yelled at for it. It is ironic though, because my dad hasn't worked in over a year, and he is still mad at me for everything I do? I can't wait to move out, and it is so close, yet so far. I'm 17 but realize that moving out won't happen for another year or two at the least. When I'm 18 I hope for more respect or I will force it. I've messed up in the past big time, but have overcome it and now that is used against me by that little brat thing I call a sister; "I get good grades and don't get in trouble like you did...blah,blah,blah". I look at it in another way though. While here you are doing a ton of HW and being a loser, I was out being a kid, having fun and getting into mischief.
In your situation. TALK BACK and be a pain in the you-know-what kind of kid. Cause trouble (nothing too serious) and make them notice you more. I know when my buttons get pushed now, I yell back and won't talk to either of my parents for days on end. The silent treatment basically. Ignore them and eventually they will come to you, which has worked well for me in the past.
Oh yeah, ride your bike to the bank and open an account. OR keep a very detailed record of your paystubs and what you spend your money on. And then when your parents steal again, notify the local police. Taking YOUR money isn't right and it's illegal no matter how you look at it.