Depends what you're after! The boss is right but both options are viable, depends how much you care about the music and how much you want to spend.
The kenwoods would be an improvement over the standard speakers which are very very harsh, the door speakers a bigger improvement still but far more subtle.
If you're planning to use the head unit to run the speakers i would suggest just replacing the speakers in the dash, you won't get much more of a benefit installing door speakers, but if you're gonna be spending money on amps and subs i would look at the door speakers, if you can afford it.
I chose two way kenwoods for the dash in my Silverstone (£40 from Halfords, haver to drill new screw holes but it's not tricky), they seem less bassy than the Sony or Pioneers that i compared them too but offered greater clarity.
Recently listened to some newer Sony Xplodes though and would probably get them now.