Lens for 2 reasons
1) I heard that the HiFi wasn't even that good (i think it got bad reviews)
2) That lens is not really a consumer item but more in the high-end/professional end, thus it is MUCH less susceptible to being marked down around the holiday season. The HiFi on the other hand is a very main-stream consumer friendly product and is more likely to be marked down. Thus you can technically get both, of course having your parents get you the more expensive of the two.