It doesn't matter, mostly.
I would suggest leaving them in the larger working space (pro photo), as the printer does have some gamut outside of Adobe RGB (1998). Photoshop deals with mapping colour from your working space to the printer space - there's no need for you to send it in one or the other. The only time that becomes beneficial is if you're not using a colour managed workflow and instead you are using the driver to control your colour. In that case, the driver typically has different options, some of which will expected Adobe RGB (1998) and some sRGB - sometimes they're labelled in a way that helps, other times they're not (and if not, I'd suggest they are looking for sRGB only).
But, as I said, with a colour managed profile using ICC profiles and with PS managing the colour, it doesn't matter except that if you use a space that is smaller than the printer's then you risk missing out on some of the printer's gamut.