For me, Resistance: Fall of Man. If 2010 counts, then MAG. Resistance 2 and Killzone 2 come a close second.
Yeah, if only 2010 did count, Resistance 2 multiplayer was absolutely amazing back in the day, not to mention the singleplayer was so fucking good too... I wish Insomniac would revisit the franchise :( As for MAG, it was such an ambitious game and I loved it! What faction were you in? I started with SVER since that was the "cool" team, but gave the other two a try and found out I actually enjoyed Valor the most so I stuck with them... my Move controller got so much use just from this game alone!