you'd really have to decide which make you want to go, Intel or AMD, before someone could give you an opinion. What motherboard will you be using? RAM, GPU, etc? If you're looking for a generic answer, the E8400 will do everything you want, unless your using multithreaded apps, then a quad. You're gonna get faster performance out of Intels, used to be better price out of AMD, but that doesnt even neccessirly hold true anymore.
If you provide a budget, a main uses of what you want a PC to do, and a CPU make option, you'll get more detailed answers.
No offense, but right now, the way you've posed your inquiry, it'll just spin into an Intel vs AMD and Quad vs Dual Core thread.
There's a ton of those in the folder, peruse them.
Penewah!
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