price performance wise the amd processor is in the lead, but if price is not an issue intel still leads. also check the memorycoin performance database: http://agran.net/memorycoin2_calc.html
In that case, performance/watt is more important. You still have to take the upfront cost, but first-order effects tend to dominate 0-order effects over time :)
It factors into the length of the breakeven (on the hardware investment) period, which can be a big deal. Not just because return is slower, but also because in a market as volatile as Bitcoin, who knows if a projected 6-month breakeven period will ever actually break even? Breaking even sooner dramatically reduces capital investment risk.
(A low price-to-performance ratio, or conversely a high performance-to-price ratio, will mean a shorter breakeven period)
