It comes down to personal preference, really. You're not going to know if glass or metal feels better to you until you try.
A couple things to keep in mind, though: glass and metal have absolutely no give, so they tend to feel bigger than silicone toys of the same size. They're also rather heavy in most cases, and so you need to be a bit more careful when you use them. Being too rough can result in internal bruising. They're very slick and smooth, though, unlike silicone which typically has some drag to it.
The Ella is pretty rigid for a silicone toy, but it's very light and easy to use. It's great if you're new to dildos.