I'm not going to answer the second question, I assume you will do the right thing.
From using 7, the biggest advantages for me are the improvements in stability and security, and the much improved hardware support.
Windows 7 is very difficult to crash, and is also very good at managing hardware devices. It will even search for drivers online and install them automatically. Thus, the out-of-the-box experience is much better than XP, where you sometimes have to struggle for hours to get all your hardware and devices working.