What is safer, plastic or glass bottles for babies?

Glass safer. The linings of baby bottles had bpa (bisphenol a) so nih & epa reviewed 700 published studies on bpa , the levels currently found in humans is higher than the levels causing adverse effects in animal studies. The U.S. Department of health and human services' center for the evaluation of risks to human reproduction has expressed "some concern for neural and behavioral effects".
Depends . Plastics have been found to contain bpa and phthalates. In low doses it is thought to cause hormonal effects and impact the growth and development of babies. Plastic bottles that are free from bpa and phthalates are available. Glass seems nice but it certainly can break/shatter causing obvious problems there.