i think you could rank the importance of three law school factors in this order:1. high class rank2. law review3. moot courtso you don't HAVE to do either of those things to do well.good grades are by far the most important thing in law school. however, if you're outside the top 15% or so of the class, being on law review is in some ways the equivalent of ranking that high. of course because most law reviews emphasize grades so much, law review members tend to be those that are in the top 15%. but your actual writing ability will usually play at least some role in the selection process, and most schools select at least a few candidates solely on their writing ability. those who are fortunate enough to make it based solely on their writing benefit greatly because, wherever they happen to fall in the rankings, being on LR gives them opportunities often open only to the top of the class.moot court, at least at my school, has nothing to do with grades. there is usually a first year competition where almost every 1L competes, where students are weeded out in multiple rounds until they have a small group to add to the moot court board. it is good for your resume and does lead to some good job opportunities, but other than that is quite inferior to a high ranking or law review membership.if it's study time you're most worried about, i probably wouldn't be. if you get on law review, i can't think of a reason that you shouldn't do it. it wouldn't require time until the second year, when grades aren't so important (especially if you're attending a higher ranked school). with moot court, at my school, the competition lasts only three days, for an hour or two each day (assuming you make it to the second round). after that, if you make the board, you are only required to compete in one more moot court competition in your second or third year in order to satisfy membership requirements. quite a few people simply sit on the board for resume purposes and don't get involved.
I admit that I don't know anything much about anything much, but I read yesterday in a comparison of law schools geared toward hiring partners that due to differences in grading curve and rank of schools it can be tough to compare candidates from different schools, especially if the school doesn't release the relative rank of the students. Moot court and law review show that the student can outperform his or her classmates and is likely one of the top 10%-15% performers. This is true of grade on or write on or performance trials.