Either way, thing to check is that (a) the network branding (if any) corresponds to the original phone, and (b) it either says "Froyo" or the radio has "_5." in the string - anything "_4" is Eclair, and it would be perverse to install that!
Also, check it says "RUU" at the start of the name, not "OTA".
But as to which, actually why not the 2.3 upgrade? If it's so the friend can get used to Android before buying their own, they certainly aren't going to be buying Froyo. Of course using any sort of stock is also getting them used to HTC Sense as well as Android.