My father-in-law is a top plastics chemist with J&J. His rule of thumb is, the more cloudy the plastic is, the safer it is. He avoids microwaving plastic entirely.
Personally, I would skip the high heat of sterilization (boiling or microwave or whatever). There should be nothing in/on the bottles except ordinary household bacteria, and those are things that your child's immune system will benefit from practicing on. Studies suggest that the reaason that farm children and children in multi-child families are healthier than only kids and indoor kids is that the exposure farm kids and siblings get to trace amounts of dirt and gunk is actually good for them.
My son went through his whole childhood with nothing sterilized, ever, because I was too tired or ill to bother, include my pumping equipment . . . no harm done. Ineed, he was rarely ill in spite of being in daycare.