I have limited experience with some of them, and I've also got a Parrot 3200LS Colour in my car and have just fitted a CK3100 to my other halves car, so I'll try and base it around facts you can relate too
Ok... firstly the biggest issue with the majority of the Bluetooth head units is the limited phonebook storage on the unit itself. Some of them simply synchronise your recent call lists (last 10 made, received, missed calls)... some of them allow you to send it your favourite X number of contacts (usually around 25-30) and very few of them allow you to fully synchronise your phone contact list so you have access to all of them from the head unit.
For me, the whole point of having a Bluetooth car kit is that I never need access to my phone while driving again. So if I'm limited to the number of people I can call, I'm slightly put off. Just my opinion though and you and others may differ, of course
Secondly, there is the issue of call quality. There are two sides to this... how you sound to the person at the other end, and how they sound to you.
9 times out of 10 they will sound great. Crystal clear, no unwanted noise, easy to follow. Sorted. BUT - It's often a different matter when it comes to how you sound to them. Some (most) of the current units have the microphone built into the head unit, which isn't ideal as your voice is not directed at that point. This means it tends to make you sound distant and also picks up too much unwanted background noise. Not ideal really.
Lastly, there is ease of use. Generally speaking, this is 'fine' with all units. It can be fiddly at first, but as with everything you get used to where the buttons are and what they do fairly quickly so it's not a huge
problem. But my advice would be play with each unit in the flesh before deciding, as it's important you feel comfortable with it
Sony, Pioneer, Kenwood, Alpine, Becker and Parrot themselves all make Bluetooth equipped head units, so you have plenty of choice. Be aware though that Alpine and Kenwood options are via an external box, which adds to the installation. I've not seen the Alpine solution in the flesh, but I've seen the Kenwood and that has an external microphone much like your current Parrot kit, so that's a big plus in my opinion.
In my personal opinion, there is no ideal combined Bluetooth car kit and headunit yet. They are getting there, but currently each of them have their Pros and Cons that all add up to not being ideal.
