I always say go with the best you can afford. Have a look at aria as they will build to your own spec and have a good reputation. I have recently been put off by Dell the fact that at work we have had motherboards, processor and power supply replaced on 5 PC's in the last 6 weeks.
I personally built my own PC so I can have what I want on the inside. I chose AMD Athlon 64 over Pentium, for a start they are cheaper, just as reliable and in benchtests out perform Pentium 4. You get some people who are Intel fans others are AMD fans. If you want to save on cost then go AMD as there equivelent chips are around 7% - 15% cheaper than Intel. AMD are often the gamers choice now but it all depends what you will be using the pc for.