Going by the review sites that have reviewed both, this is what I come up with.
Highest production values ever in gaming = Gears 2 (IGN)
"It provides a truly electric action experience, building on the original with intense, astonishingly epic set-pieces. What's more, the presentation is the closest we’ve got to starring in a full-blown action flick."
Pushing HD Graphics to a new level = Gears 2 (IGN)
"The world around you is frequently breathtaking, radiating an unmatched beauty and superb variety – far more so than the first game, famous as much for its love of brown as its brutal combat - from dense forests to haunting underground caverns, plus a few surprises along the way. It's a game that demonstrates hi-def visuals and rib-shaking sound at their very best: Marcus and the boys look fantastic, with even more detail and grittiness than the original, while the Locust look as menacing as ever."
Best AI of any game = Gears 2 (IGN)
"Thanks to some thoroughly rewarding level design, combined with some of best – if not the best - enemy AI in the business, Gears of War 2 provides an exhilarating, challenging and visceral experience that utilises the series' pioneering cover mechanic with masterful aplomb"
Best Level Design = Gears 2 (IGN)
"The Unreal Engine 3 has never looked better. Characters and enemies are bursting with detail while the levels are a masterclass in style and design."
Best atmospher (AI comes into this) = Gears 2 (IGN)
"Such is the intensity of the fight that if you're caught in the open, it's unlikely you'll last more than a few seconds. The Locust horde, especially standout addition the Bloodmount, is an even tougher, more elusive target than before. Darting from one hiding place to the next, they take full advantage of the world, using short, sharp burst attacks before ducking back into cover. There's a level of cunning on display which genuinely satisfies – your opponents actually feel like formidable enemies, not some stunted algorithm, and the sensation of war is overwhelming. "
Best story = Resistance 2 (IGN)
" By contrast, Resistance 2 is very Hale-centric, and focuses much more on his actions and what he wants to do. That's fine, but his motivations behind what his decisions are or why he chooses to act a certain way or go to a specific location aren't fully explored. As a result, some elements of the story aren't fully cohesive, and a large number of questions are left unanswered, which could potentially confuse players until the hypothetical Resistance 3 eventually is released"
Nothing more to rate.
Gears 2 - 5
Resistance 2 - 1