Prescott's were Intel's way to reduce costs of the P4 line, so they found things to remove (that reduced performance) and replaced with things to re-balance performance for cheaper manufacturing costs.
For this reason, the Prescotts generally run a bit hotter than Northwood's and their core floating point/int performance is a bit weaker. To compensate, they increased/optimized the cache on the Prescotts to bring int/float performance up to where the Northwood's performed for most applications.
I personally prefer Northwoods as they generally run cooler and while they have less cache, their core performance is a tad better so they perform similarly to CPU's with better cache.
For most home users/gamers, it really makes no difference other than heat concerns... which are really not a big deal.