one month later... I'm sure the windows are installed by now, but...
You obviously would not use a latex caulking, and to my knowledge, latex caulk is not recommended on vinyl anyway. Generally silicone or similar products work best. I have used Novagard, OSI VP275, and any type of silicone with good success. All the above will attract dirt, so they should not be used in abundance where they will be seen. For exterior caulking, I use OSI Quad, which is available in all siding colors, sticks to vinyl, is paintable, does not attract dirt.