Purely IMO, but unless you're constantly taking your phone into "hazardous" environments (parties, moving furniture, playing sports with it in your pocket, etc.) or are just generally clumsy, there's really no need for a case. They tend to just add bulk, and I find that other than a simple drop on pavement or tile, the case won't protect against the damage that would have broken the phone anyway.
For example, I had LG-something or other back in the days when the Motorola Razr was popular, and it was in a case in my pocket. We were moving a desk out of my boss's office, and it slid out of my hands and landed on my thigh. The pressure from the desk cracked the screen right through the case.
On the other hand, if you do happen to be the type that drops your phone on the ground fairly often, I'd go with an Otterbox. It adds a LOT of bulk, but it's really the only thing I'd trust to actually protect the phone. Don't believe any of the "my friend ran my phone over with his car, and the Otterbox saved it!" BS, but aside from a lot of pressure or a one-in-a-million drop screen first on a pointy object (corner of a table, etc.), it'll make a difference.