I'm a huge Singletary fan. The guy has an amazing work ethic, never stops trying to get better, and even hired a speed coach to try to get faster.
He makes plays every week for us on offense, both catching and running. He has elite elusiveness and a good burst. It's the lack of top end speed that keeps him from being great, but IMO he is a very good back.
He'll never be a top RB in the NFL for that reason, but he has a lot of value and does a lot of things well.
It should be Singletary as #1 and Cook as #2, with the hope being that those roles switch but both are here long-term.