there are a lot of differences but the most common one is the fact that bitcoin has succeeded in becoming a real currency and fullfill the cryptocurrency role but altcoins have always been only speculation tools to get pump and dumped.

there are more technical differences too. like the blocks, the mining algorythm, the block size, the block time,.... and a lot more. you see it is not easy to compare bitcoin versus all the altcoins in general this way because the differences are sometimes so many.