In my experiences:

Falls Creek > Malletech > Yamaha > Musser/Adams

Old glocks are low G, newer ones are low F, but the best sets extended lower and upper ranges.

Big bulky case = good for resonance

High quality instruments have lots of overtones. If you listen to them up close, it may sound hazy or unfocused. The overtones will not be a problem at a distance and will enhance the ensemble sound.

Bells with a pedal have (in my experiences) been referred to as "song bells". I don't like these so much in an ensemble setting.

Carts are important, but there are more options than what is available for marimbas and vibes.

This is also a great time to address your mallet inventory. Your students may have their own bell mallets, but I believe ensembles should stock bell mallets with phenolic, lexan, and brass heads.