Absolutely Osk Kosh holds up the best! My oldest son wore Osh Kosh - 15 years later we got the clothes out and my youngest son wore the same clothes, they still looked "in style" and were in great shape!
Rachel -- my personal experience is that yes, OskKosh does hold up very well when it comes to their denim. I usually use there's and GapKids stuff whenever I can find it on sale. Plus the little tabs that adjust the pants are good quality too!