Going to Chelsea : + better salary and bonus + working with the special one + better chance to win the trophies for many years - obvious 2nd choice striker behind Costa Going to Arsenal : + 1st choice striker until December guaranteed - if not performed well until December, will be the 2nd choice behind Giroud anyway - less salary and bonus - working with special(ist in failure) one - fight for 4th place trophy If I were him, not that hard to pick the right move.