I don't know too much about Bluetooth GPS receivers, but I'll try my best. The biggest thing I'd say you will want is a large power capacity (or the ability to power it via a cigarette lighter). My Garmin (a handheld unit, but it rings true for a PPC unit too) has run out of batteries before (on my way to Chicago from Detroit), and it was a huge pain in the ass. So whichever has the highest battery capacity (or the ability to be powered via a DC jack), I would automatically recommend. I can't say I've had any experience with Globalsat vs. HAiCOM, but I've at least heard of HAiCOM, and with GPS units, brand names can sometimes mean quite a lot.
I think nearly any GPS receiver will be able to lock onto satellites very well in a car, but the most important thing is to get good software. When you get a GPS unit, as long as it's NMEA compatible, you can use ANY software with it. It's kind of like buying a CD burner...they all burn in the same way, so you can use any CD burning program with it.
Use windshield mount...it'll give the unit the best visibility of satellites. Plus, vent mounts obstruct that nice warm or cool air from getting to your face.
I think the more important decision here is to research the software...the GPS hardware might be great, but if the software sucks your whole GPS experience is going to suck too. For navigation, you'll definitely want voice-guided navigation. Also, different map views will be important too...it's a personal preference, but I prefer maps that look like regular paper maps; all this "bird's eye view" mapping crap is annoying, IMHO. But yeah, definitely choose software that suits your navigation habits best, as the software differs more than the hardware in most cases.
Again, I don't have much experience with PPC GPS, but I think that should at least be enough to get you started on another goose chase after some good PPC mapping software.