Bosch is usually better. buy those with stainless steel interior. it will last longer. (longer is like 15-20 years) The one my parents are using is Bosch, it has been 10 years now and still like new.
you MUST rinse the plate before put in dishwasher. It is so easy to do. Generally speaker, no matter how oily the dish is, dish washer has no problem clean them.
Detergent is VERY important. from my experience, Cascade Complete work the best. u must try this before anything else. it is not expensive and work very well. (a bottle cost USD$5-6 and can use for 3-4 month if use everyday)