I'm running 215/35-19's and I did have one go flat due to my error. but if you are constantly losing air pressure you may want to have the wheel inspected. If you bought them used they may have a crack in the wheel itself causing the lose of air pressure? I had the same problem about 3 years ago with my other car running low profile tires after a flat, came to find a stress crack which was causing me to lose pressure.. Your local wheel /tire shop should be able to run a test for you. As for tires I've had Toyos, Nitto, Yokohamas, and Falkens. Nitto's gave the best performance for the $.
Kevin