I can't be a perfect judge of this because I can't make a direct comparison but I guess it depends on what you are using it for. In most cases, both drives will perform about the same, however the difference lies in the sustained transfer rate. 5400 rpm drives are likelier to transfer at a slower rate the longer they are being accessed so if you are, lets say, opening HUGE photoshop files or moving other large media for a long period of time, then it's probably better to go with the 7200rpm. If however, you work with smaller files like say an indesign or illustrator layout then it's better to go with the 5400.
If you're concerned about storage space, get a external hard drive, it'll save you a lot of grief (at least it has for me).