Fairly quantifies the action. eg. It is fairly quick. "It is quite quick" - not too slow or too fast, just a medium or slightly above average speed compared to others. "My horse was fairly quick but he didn't win the race" "I am fairly sure that that is the right answer" - I am not certain but there is a higher than average probability that I am right ;) Rather can be used in the same way - "My horse was rather quick" "I am rather sure that that is the right answer". I would always use fairly (or quite - depending on my certainty) in this scenario. Rather tends to be used by the upper-class and depending on how it is said may be perceived as a little pompous (NB. This is my perception - am i allowed to say this? Would others agree/disagree?) Rather can also be used when referring to preferences. "I would rather go somewhere else" "I would rather not go" "I would rather run than walk".

"The job is fairly easier but it's rather difficult for me." that is what i would answer to when comparing to a previous job i have done. which means, the current job is easier than the last, but its difficult for that person. hope that helped