In truth, there are advantages and disadvantages to either type. For example, stainless steel bottles offer a lightweight and easy to clean option for your water bottle, but they can also become a bulky dead weight when empty. Plastic or silicone based water bottles, on the other hand, often can change shape depending on your needs and the amount of beverage contained within them. Their portability can often be quite better.
As a drawback though, they aren’t often dishwasher safe and can degrade over time. So the real question is what is the right type of water bottle for you. And to answer that, you need to consider a number of different factors including how you are going to use them, what your storage needs are, and how long lasting you need your water bottle to be.