When I shop around for a cpu, i like to set a budget, and then narrow down the choices of my CPUs. Then i evaluate each of the candidate to determine which one has better value. I usually do this by using a rubric and grade each cpu on a scale of 1-10. 1 means i won't buy while 10 means i will definitely buy.
For example, if i have $120 budget, i can narrow my selections down to AMD fx 6300 and i3 4170
i3:
Slightly better performance in gaming than fx 6300 on average +2
Much better performance than fx 6300 in older single core games +3
Lower power consumption and thermal +1
More recent and modern architecture +1
MutiThreading +2
Made by Intel -10 brand loyalty penalty
socres: -1
Verdict: no way would i buy it
fx6300:
More cores +2
Future games support higher cores thus a bit future proofing +1
Great mutitasker +2
Overclockable +2
faster than i3 in mutithread +3
scores: 10
Verdict: this will defiantly be my choice for $120 cpu