When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I would always start with the headunit. Fitting better speakers will make a difference, but they usually require more power - and you need to spend a reasonable amount of money for a decent speaker upgrade. I dont know the power output of your headunit, but even with factory speakers, an increase in power will make an improvement. The order would be then:
1. New headunit
2. Sound deaden the doors
3. Replace speakers
Others may disagree - but then, its a bit like "should I increase the processor speed on my Pc, or buy more RAM?"