Need your help for a decision...

[rakers]

Hey I recently bought a Pontiac g5 gt from a local dealer, it ran good and realized my rear brake lights and rear blinkers weren't working. I took it to my mechanic who found out it was because a dumb ass installed a towing hitch and wired it wrong so the wires melted and shorted out the system. My mechanic performed diagnostics and fixed electrical issue. My g5 has been using a lot of gas ruffly 280km to a tank, my mechanic informed this may be due to an oxygen sensor that needs to be changed.

I went and informed the dealer where i purchased the car from and he informed me there is nothing he could do due to no proof that the problem was prior to purchase. He stated he could offer me a 2006 Chevy Cobalt and $500 as a trade for it.

The Cobalt is 2 door coupe LS just basic with no power option.
The \G5 GT is much nicer with 4door heated leather seats, sunroof, power windows and locks with keyless entry, an alarm and stock pioneer sub.

I dont know which choice to make a Cobalt with nothing wrong with it and 64000km or a Pontiac G5 GT with 90500kms and needs the hand brake fixed and a new o2 sensor.
please help me make my choice