Journals versus law review, in general? Are editorial positions on journals worth it? Does it really matter on your resume whether you're the X Editor (unless maybe you're the EIC) or an article editor?(Warning: some of this applies to HLS specifically. All of it is my jaded, biased opinion.)
I didn't make the law review. In retrospect, I should been more focused when I took the competition, although it's probable that this wouldn't have made a difference. Despite the occasional obvious omissions and AA, the law review seemed to do a good job of selecting the best and brightest. It may come as a shock to learn that you are not among the best or brightest in your class. Contextual mediocrity is a bitch.
Instead, I spent a lot of time on a specialty journal. My thoughts on that are here. Many of those thoughts are bitter and snarky, mostly because the average specialty journal staff member puts in very little work. This is good if you are one of those staff members, since you can get some marginally useful resume fodder in exchange for a small time commitment, but it is bad if you are in charge of those staff members. I basically burned out before our second issue even hit the presses. Being EIC of a journal was very helpful, resume-wise, but I might not have needed that help if I had spent the hours consumed by worrying about galleys, author contracts, MIA editors, and obscure Bluebook errors on classes.
If you take the law review competition, be serious. Don't move to a new city the day before you start. Don't start a new job and try to do it at night. Some people do this and still make it. You will probably feel better about the result if you clear that week of other commitments.
If you don't make law review, and you don't have a burning desire to work with legal scholarship in a field for which there is a specialty journal, just forego the journal experience entirely and focus on your grades. Many people who are not on law review get excellent clerkships and jobs. Those people almost always have really amazing grades. I did hear some anecdotal evidence of some people's GPAs declining after they made law review due to the time it demands, which essentially equals a part-time job. Being on the editorial board might compensate for less than stellar grades. Being a generic HLR person might not.
People say grades don't matter if you go to a top school. Those people are either full of crap or they already have a job lined up. Law review is great. Journals are nice. But unless you're willing to backstab your way to a top slot and are obsessed with legal scholarship, you're better off studying for exams and taking some clinicals you enjoy. Shoot for magna.