Despite his stellar year in 2014, Murray is very underrated. So many are quick to credit the Dallas offensive line for his production last season, but his efficiency over the duration of his career has remained steady. He was more or less as good in 2014 as he's ever been, but several contributing factors (including improved O-line play, health, etc) lead to his dominant statistics.
Having said that, despite the fact Murray is an excellent RB, McCoy is the superior talent. I'd welcome either on the Bills from a talent perspective, but if I could choose I'd choose LeSean.