None of the PC manufacturers can really prove that they are better than others.
One should first look for the configuration he needs. Normally today people simply need a P4 with 256 MB ram, 80 GB Hardisc with CD RW & speakers with a good processor speed.
This configuration is available with all the manufacturers including the assembled ones.
And one should look for the price & the buying convenience(including after sales service). Many retailers claim to be providing after sales service, which many can’t really do. So one should try confirming if they are really into hardware repairing or not.
If your system is troubling you, many servicing people simply suggest formatting & reloading, which means they cannot rectify operating problems.
Nowadays when the price gap between some of the branded PCs & the assembled ones is nullified, then one should preferably go for warranted/branded PCs e.g. HP, HCL etc.
IBM has been taken over by Lenovo. And remember that Lenovo & Acer are basically chinese products now.