I guess I should have been more clear about what I meant. I meant if It ever came down to having to pick one of them. Ran or Shiho. I don't believe that Ran is useless and she definitely has her strengths but I do think that when things get dangerous Shiho would be more of help for
1. I can only believe that in Shinichi's career cases are only going to get harder and we all know when things get heated Ran is always thinking about him, praying that he would save her. Ran can handle herself against a purse snatcher but as Shinichi develops as a detective I think there will be a lot less of those.
2. Shinichi and Shiho's relationship is one of hatred and love. Guilt and trust. If things ever go wrong she never waits for him to save her, she can handle her self like she proved time and time again and that is why Shinichi chose her as his partner. He can trust that she will make the right decisions. Unlike Ran he doesn't have to keep her by his side the whole time so that she wont get hurt.
3. As we all know Shiho is very skilled with a gun. And being brought up by the Organization you can assume that she herself is also quite skilled at fighting but I guess we don't know for sure.
Also I don't believe that Shinichi would ever just let her go but I don't see why she would stick around. If she was the one that decided to leave then he has to make a decision Ran or Shiho.