which is better?

[RobNJ]

Mice are notoriously a pain in the rear, frequently are aggressive towards each other and are MUCH more sensitive/easily stressed, and therefore tend to have more issues being good mothers.

This is obviously a strong(and misfounded) opinion...I've been breeding mice and rats for well over 2 years now and have never had an issue with mice being aggressive, having maternal issues, eating babies, etc... Maybe I'm just lucky, but after 1,000's of mice, I don't think so.