There's a very wide variety of packages available at different international schools. Some have a very high turnover rate and teachers often leave after 2-3 years, the better ones(HKIS, CIS, CDNIS, ESF, GSIS) are good and the students are terrific. You'd likely make more money but it's not easy to land a job in the better schools with only three years experience unless you have something special to offer or you know someone.
If you're serious, you can either take whatever job for a year or two and then get a feel of the place and which school you really want to end up in. Otherwise, hit the job fairs in February.
My experience of people leaving HK is rarely because of work conditions. It's either because they miss home, have kids and want a different environment, some of the ladies find it difficult to meet good men here, tired of the pollution and small flats....