Look at what voice parts you have available in your choir. You may not get a lot of guys (if any) to try out for and enroll in your group. You may have a ton of altos and no sopranos or vice versa. Based on these numbers, limit your selection list to only those arrangements that fit your choir's composition.
Consider how many people are in the group. If your school is very big, then you might be able to tackle large works like the Mozart Requiem, or pieces that require a lot of division of parts. Otherwise, you'll need to stick to shorter, simpler arrangements.
Look at the age of the members of the group. If your guys are mostly seniors who already are comfortable singing deep bass, then you can pick music that has a wider vocal range. If your guys are mostly freshmen whose voices still are cracking constantly, stick to pieces with minimal movement that avoid large leaps.
Look at the language of the arrangement and how often the choir meets. If you are looking at a piece in a foreign language and only meet for half an hour on Mondays, then you may not have time to work on learning both the music and the language. But a piece in your native language may be workable in that time.
Look at the season or whatever is popular at the time. For instance, an arrangement of a song by the Dave Matthews Band may hold the students' interest far more than a madrigal from the 17th century, simply because they're probably already familiar with the Dave Matthews Band song and consider it "less nerdy" than a madrigal.
Figure out if the piece you are considering relates in some way to the vocal techniques you want to teach. If the students won't develop from the piece, don't choose it.
Look at your budget. You'll need to purchase original copies of the music for the choir in order to follow copyright law. Larger works always are more expensive than short pieces, so if your choir is particularly large, it may actually cost less to fill your concert with small works.