Except for the pair where DD poked pencils into the crotch while having fits in school, Cat & Jack from Target have held up the best for us. We've had several pairs for two years and my DD is super-active - sliding, roughhousing, running, jumping, mucking about, etc. What I love about them is they have reinforced knees, so I'm less concerned about DD wearing through them before they're outgrown.
I've also been pleased with the leggings from Primary.com, but we only have a few pairs because they are spendy. Fabric weight-wise, they remind me of older Hanna Andersson and have held up fairly well so far.
For softball, definitely get softball pants as leggings will NOT hold up.
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Liz
DD (3/2010)
"Make mistakes! Get messy!" - Miss Frizzle