personally, i didnt do it, but i would go the instructor route. whether you beleive it or not, there is a lot of time between where you are and the right seat of a 7-4... that being said, having a CFI and actuially using it will show you what you really dont know and should know about flying, as well as reinforcing the basic concepts of flight day in and day out... you'll get to know the regs better and be able to communicate effectively about the airplane... lastly, i think airlines like the CFI route better becasue eventually you will become a teacher at an airline in that you may be a senior Captain and have a new hire F/O who you will essentially need to teach.
just my $.02