I bought some Crocs stocks (CROX) a while ago; actually I looked at Under Armour (UA) at the same time and I am glad I made the correct decision (so far). Besides the difference of PE ratio, CROX is 42, UA is 76 (supposedly the lower PE means the price is cheaper). I made this decision more based on the business prospects.
From my observation, Crocs are sold in a lot more stores than Under Armour, which are only sold in Sporting Good stores. In other words, Crocs have a wider distribution channel. This is very important for consumer goods. By the same token, I found Crocs have a wider appeal to consumers, especially kids. Under Armour has made efforts to reach women and kids but they are not there yet.