It's MUCH more important to go to a place you may want to go as a resident on at least two levels. As an FYI I did away rotations at two very well known programs, and got good letters from both of them. They were both programs I was very interested in attending (and turned out not to be where I ended up going.) However, that's not the most important thing. Good letters from most programs with a residency will help you out. And if you're interested in a certain area, getting a letter from in the region will definitely help.
One, you may find out you either do or do not want to actually go there which will be a huge piece of information for you. One of the hardest things about the match process is trying to get a "feel" for a program from internet reviews and an afternoon interview there. If you think you want to be at a place, spend a month there, and that decision gets a whole lot easier.
Two, if you DO want to go there, doing well on an away rotation will likely help your chances. If you've got a moderate application, but then blow people away (figuratively) on your away, that's likely to bump you up on the rank list. We've had a couple of people who've moved way up the list based on knowing them from their rotations, their work ethic, personality, etc.
As an aside, remember that often the "best" med students do aways at the "best" programs. It may be harder to "shine" on your rotation if you're surrounded by some of the best applicants in the country. Also, these rotations tend to fill up pretty early as I remember as they draw the Type A crowd. A lot of these questions have been discussed at lengths in other posts on this forum. Use the search function and you should come up with some useful information.