As someone who has contributed many articles to magazines about radios in general (and about car radios in particular) I'd laugh at the suggestion that any of those makes are the 'best' (while, at the same time, conceding that they're all perfectly reputable and of high quality). For me, Blaupunkt outranks them all.
Most factory fit stereos these days are actually pretty good quality to start with and there is not a lot to be gained by changing them (unless you really need a certain feature that the current stereo hasn't got)
Speakers are a different matter though, I'd say you'd gain more by changing the factory fit speakers to something decent rather than the head unit.
Chuck is right about the speakers. However the Panda is a low cost car with probably a low cost head unit. There may well be an advantage in an upgrade here too.
You do get a lot offered on ebay so can afford to upgrade very reasonably!
I am thinking of upgrading mine now for the Spitfire. Im do not really need CD but USB/iPod would be good. I have a separate amp so power is not important just 4x RCA outputs
I will be bidding on one tonight then hopefully I can recoup the outlay when I sell my curent one.
There are loads of units suitable for your Fiat at the moment.
I won it! Got a lovely (I hope) Blaupunkt Memphis for £71
Now I have a Top range Pioneer for sale. 50w x 4, 4xRCA line outs, Plays MP3 discs too. Lovely condition. Interested?
Just seen also that Blue Spot car audio are selling a Blaupunkt Valencia for only £69.99 delivered.