A Sigma or an '89 Mitsubishi Colt?
They’re both in the same state of repair and about the same price so would there be any reason to chose one over the other?
I hate buying things when I’ve got no idea! I wish everything was as easy as buying a computer! 
What’s a Sigma?
Anyway, With any car that old you will need to have repairs done every now and then, so the best car will be the one that local repair shops are most familiar with and where spare parts are available and low cost. I’d recommend you go to a parts store and ask for prices for common items such as waterpump, timing belt, brake pads, exhaust system etc and compare prices and availability. Also, if you have a mechanic you used in the past, ask for their opinion on which car is the most reliable and easiest to work on.
/Markus