xWinForms is easily the most complete and actively maintained GUI system for XNA. Window System for XNA (WSX) had some good progress in the past (I was working on it for a while), and is still a decent system, though it hasn’t been maintained for over a year now. The best option is definitely to go with xWinForms, at least until WPF interoperability comes along (next version of WPF/XNA?) and makes all the other options effectively obsolete.