Ah...the discussion here reminds me of another thread on this forum...
I'm not counting all the discussions regarding events prior to say, the late 80's as it seems to be stuck fighting over single points (trees for the forests) rather than the war as a whole.
I have two theories, one assuming, for whatever reason, the (highly unlikely) non-use of nuclear weapons, and the second assuming the use of nuclear weapons. And, again, both assume a military state of readiness of the late 1980s to 1990s.
1. [Assuming a conventional-only conflict] USSR/WarPact invades western Europe. Simultaneously, they push the North Koreans to invade South Korea to tie up American resources and launch an invasion into the Middle East to secure oil reserves. Already there is a lot of assumption; could the Soviets have managed all of this without western intelligence finding out? But moving on...
The USSR, given some level of strategic surprise, rolls forward with massive armored presence and strategic bombing of key locations and troop concentrations. Initial gains would be more than they suspected; though it pains the NATO allies, they give ground in order to deal more damage to the invading forces, but NATO needs time to bring reserves to the front and reinforce their troops. The US is hampered greatly, given their relative weakness in airlift/sealift capability, which is being stretched to the limit as it deploys reinforcements to Korea and Europe and is tasked with deploying in rapid fashion the RDF to the Middle East. The Soviets/WP drive deep into Germany, until a counterattack stabilizes the front somewhat. As reinforcements stream in from both sides (Cat2 and Cat3 Soviets being called up to serve as follow-on and rearguard; US mobilizes Reserve and NG forces en masse, but are needed in front-line action).
Eventually NATO achieves a workable level of air superiority (crucial to the AirLand Maneuver strategy) and pushes Soviets back across the West German frontier - by now, the USSR/WP central command is being hit by deep-penetration bombers, cruise missiles and stealth bombers and C3 is disrupted in large part. NATO's air and sea assets neutralize the USSR/WP air and sea assets but are mostly neutralized themselves due to losses.
Without the large air presence, NATO's drive to Moscow is stalled, and the front in Europe is a static line, as both sides change their strategies continually as losses mount.
In the final accounting, Europe is left a devastated wasteland, as is Korea (which I believe would fight to a stalemate at roughly the 38th parallel) and the Middle East (although which side will control the oil reserves is uncertain - the Soviets would likely have control of territory into Iraq).
2. [Assuming use of nuclear weapons] The war begins much like the conventional only scenario, but as losses mount, NATO and WP both use tactical nukes to shield retreats or withdrawals. Eventually, both sides unleash their strategic arsenals, devastating the entire world. In this case, no one wins.
When I was in the Army, the junior and mid-grade officers would wax poetic about what would have happened if the "big one" happened. We spoke of how the US would certainly win eventually, given the technological advantage arrayed by the west (and of course, we'd been trained to believe we were the best). One time, a Colonel dropped in on our conversation. He essentially said we were right. The US would lead NATO to victory, but it would be hard fought. He pointed randomly to all of the officers there, except two (there were eight of us) and said, you'd all be casualties. Our families would be decimated. The enemy would be even worse off.
My theory is that both sides during the cold war didn't really want to fight a massive war in the end (though they planned and trained for it constantly). The powers that be on both sides had to realize that there was no way to start such a war without billions of lives lost as a result, not to mention the absence of any "pre-war" global superpower.
I've given it quite a bit of thought, and while I come to the conclusion the US would prevail, the cost would be unimaginable. I'm certain we could all agree to that last point.