THE prime lens

Hi,

I shoot with a 5DII and mostly the 24-105L and 70-200 2.8 IS II

I really like the pictures from the 24-105, but it is relatively slow at f/4

I love the pictures from the 70-200, but it is sooo big for everyday walk-around use.

I would like a fast, reasonably priced walk-around prime.
I have a Canon ef 50 1.4 and am not satisfied with the shots from this lens.

I'm thinking about Sigma 50 1.4

What do you think?
Which is THE prime to have?

thanks,
Michael