I say both are good, but if you are like me, playing NV first might sabotage playing FO3 later. Case in point, there are some perks and mechanics introduced in NV that are not in FO3, which for me made playing FO3 a bit more tedious and overall less fun, but I still liked it. Also to me it felt like FO3's locations did not have a whole lot of variety to them, but that's just me.
Also of note, for whatever it's worth, FO3 uses Games For Windows Live, which is on the disc version of the game and I'm pretty sure it is on the steam version as well
Also of note, for whatever it's worth, FO3 uses Games For Windows Live, which is on the disc version of the game and I'm pretty sure it is on the steam version as well