I don't think it's as easy as saying Acer is better than Dell. Depends on the model. You can break any laptop down into its component parts and you will find different quality components used in each model. As mentioned above I've heard a lot of good things about Dell's 'complete care' warranty. I have more or less given up promoting any one brand except IBM. IBM's reliability and service still remains top in my opininon.
The real point is, if you've done your homework on components, and barring a hardware failure, you should be happy with whatever brand you choose. I can only say that my Ferrari has really been the best computer I've ever used. For once, it was a laptop that did live up to all the hype.