Thomas Hardy Biographies

What Thomas Hardy biography is considered the most critically sound? I've heard good things about the Millgate one, but I wanted to make sure before I invest a lot of time into one. I'm writing my undergraduate thesis right now, so I don't have a lot of time to spare :P

Millgate is a standard. Also recommended seem to be Hardy (1994) by Martin Seymour-Smith, and Robert Gittings' Young Thomas Hardy (1973) and The Older Hardy (1980).