I'd go with the XBOX 360 to be honest. XBOX Live became a very robust service that Sony spent much of the last generation trying to catch-up with.
Given the huge brand loyalty Sony had from the PS2 generation, it's staggering that the 360 managed to end up on fairly even footing with Sony, and was even ahead of Sony at times, for most of the last generation.
XBLA also really forced Sony to review the way it treated independent and smaller developers as well as apps.
The 360 really caught Sony off-guard. At the beginning of the generation it really felt like Sony just assumed that "better hardware" and the "PlayStation logo" would ship consoles.
For me, as much as I've owned each PlayStation console - I actually even bought a XBOX 360, which is telling considering during the PS2 era I thought XBOX was scum on earth and Microsoft cashing in on a market where they weren't wanted. So I have to say it was the 360.
The tables really flipped with PS4/XBone though.
Although in terms of opening up the market and diversifying it: Wii hands down.