Some people go to some of the big box stores for their computers when they need one. One-Stop Computer Services offer custom built computers for prices that are comparable to the big box retailers, but with higher power and increased relevance over time.
When it comes to performance for the price, AMD is the clear winner of this race. They tend to have a higher power draw than Intel processors, which will mean higher electric bills will result. How much higher will depend on how much you use your computer, and for what you're using it.
Most of our computer builds use the AMD FX-Series processors. They are work-horses that will do any task that you ask of them. Generally speaking, we use the 6 and 8 core variants, which you are unlikely to find in any retail build.
When we're building an Intel-based computer, we use the i-series Haswell Processors. The Haswell processors not only have great performance, they have extremely low power consumption, compared to an AMD or their previous generations.