Which is more effective for anxiety. . .5 mg Valium or Buspirone HCL 15 mg?

These vary a lot from person to person, best accurate answer would come from the prescribing physician, otherwise it's a best guess. Let's not guess on something that may possibly make things worse.

I would use the Valium. It is better for short term anxiety producing events than buspirone.

You cannot take buspirone on an as needed basis so for this purpose you will need the valium. Buspirone has to be taken on a regular basis to prevent anxiety. Valium treats the anxiety. I suspect that part of your phobia is how you think of it. a needles shoved into all the way into your shoulder is not a pretty thought and you will dwell on it all night, won't you? I had medication injected into my shoulder and it wasn't anywhere near as bad your thoughts are making it.