I had Lydia be a blade just out of curiosity, and going to stick by it for now. I think I'm also going to have the dark elf at the drunken huntsman be a blade as well as the elf that hangs around in riverwood.
For me, I try to get the weak characters to be blades and the strong characters as my personal companions now.
I love Lydia to death, but seeing her getting killed over and over again in Markarth and restarting up the same game for five times got frustrating finally.
All the characters should be getting blade armor and weapons anyway as well as any equipment you first issued them; they just won't be using the old equipment.