You can probably guess; Ubuntu. I wanted to check out Unity. I ended up going with Mont though. Windows 7 doesn't come bloated as far as I can tell, but I built the PC myself and installed an OEM version, so no third party bloat ware. I realize this is atypical.
Ubuntu isn't bloated, really. It certainly has less bloat than Windows 7. However, it does feel very bloated when you initially install it, simply because it has to fetch so much stuff from the network.