With both cars around or over 200k I would not call either reliable.
Either of those should be considered an around town car only.
For long distance driving I would say neither would be considered
reliable.
Next is what is going to be more expensive to fix as with 200k they
are both going to breakdown. The Cavalier is going to cost much less
to fix when it breaks down. The BMW will cost an arm and a leg if
you need work done to it. Also being foreign you have to find a mechanic
who will work on it.
If you can not work on cars the Cavalier is the only one you should get.
BMW costs of ownership for repairs and maintenance go up very rapidly after the first 60000 miles. More then likely the repair costs per year on this car could be enough to buy a Cavalier and replace it when it brakes down then to keep the worn out BMW on the road.