There really is no AMD CPU right now that is as fast as or faster then the Intel I Core processors right now.
But a quad phenom II will be faster than a dual i5 in many situations. Multitasking suits a quad, but with web browsing you won't notice the difference.
For general use, the most important speed factor is the storage because this affects boot and application launch times. An SSD upgrade would have a transformative impact on your computer but it's an expensive upgrade.