He's still free, but he chose to come back. I think that if the house elves want to work than they can but they should get paid or aloud many breaks. I think the elves should decide on what they like, although letting them work make them happy, too. But for Dobby, it's okay to be paid, so elves can get nicer clothes and maybe soon own their own house. I also agree with Hermione, but I won't force them to be paid.
Elfs DO like being servants.
You'll make them miserable if you take it away from them. The Weaseley twins are right. I think If a House Elf wants to be paid, it should be paid. If a House Elf doesn't want to be paid and doesn't want to be free it shouldn't. I think the Weasley twins are right.