What do you prefer for a string concatenation and why ?

I prefer & because
- it shows explicitly what the code is supposed to do.
- it forces a concatenation even if the variables aren't
declared as string.

A collegue of mine insist on using +. He claims it's faster, (which was true in vb4 but not anymore in vb5 and up) and better in general because & is a variant operator which you should avoid. This wouldn't be so annoying if he hadn't developed the habit of scanning all code on & and changing them to + which becomes very annoying after a while.

So what do you think ?