Setting a single key as my leader 10 years ago has been really nice. Personally it is back tick for me, but space is probably a good one too.
Does it ever create issues for you if you need to type the backtick in the terminal?
I found that Ctrl-A does a great job: it is conveniently located in relation to other keys that I need to interact with after I activate the prefix, and is in general easy to use.
I've been using Ctrl+Q, it replaces an almost completely useless key combo (flow control if I'm not mistaken), and is easy to press.
bind C-a send-prefix