a throttle body spacer will give you next to nothing for gains, maybe 1hp if your lucky. with a throttle body spacer it will push your CAI tube even closer to your strut tower and could cause some fitment problems with your CAI. on the other hand, the intake spacer does have quite a bit more gains than a throttle body spacer
steer clear of the tb spacer, they have been known to cause problems in V8 cars, and the idea is the same, also, they whistle very annoyingly. Go with an intake spacer, there are dyno proven gains with them and i have never had a problem with mine.