Hmm. My favorite is better than your favorite because I say so. OK.
The British were handicapped by their government policies. They tried to adopt new rifles before WW1 and again before WW2, but failed due to the outbreak of war in both cases. Even they realized that the Lee Enfield was not the greatest rifle in the world (I am not sure why literate and illiterate armchair historians still argue about it). And yet, they fought very well with it. More of a case of using what you have rather than whining about what you wished you had (this latter one is something that seems to plague many armies, even the US). And the fact that it enjoyed a long service life had more to do with the aforementioned government policies and the starry-eyed belief that the last war was so horrendous that no one would think of starting another (if you doubt this, read up on British history, the peace movement, and Neville Chamberlain).
As Kraig pointed out, by 1917 most of the combatants were stalled by tactics, supply shortages, and just tired. At that point, the Germans held more ground, had fewer casualties, had better morale, and were generally "winning". Then the US joined in, and although they were not welcomed with open arms, they brought new men, new weapons, and most importantly, new supplies of food and materiel. US soldiers were used to relieve French and British soldiers from cooking, laundry, stablery, drive trucks and ambulances, fill in and dig trenches and fortifications, and in general just pushed out of the way and into menial jobs by both the British and French in a huge display of nationalistic pride. The French and British had agreed to arm and house them, and did so initially until Pershing managed to tick everybody off. Once in battle, our tactics were a huge surprise to all parties in the war, mostly because we had little or no formal battlefield training, we just came in with enthusiasm, operated unconventionally, went around obstacles instead of trying to go up against them, and started killing Germans. We learned, we adapted, we overcame. That's kind of what happens when you throw 2 million men into a stalled war. The French and British should be grateful we did not join the Germans instead.
As far as who won the war, the French and British had pretty much used up their available pool of conscripts and could not move the Germans, so they could not win the war. Germany started the war with a huge technological and logistical advantage (French had little heavy artillery, British still used black powder in their artillery shells, and Germany had huge rail networks to supply the army with what they needed) but lost the war by not paying attention to where their food was supposed to some from, their crops were insufficient to supply the vast army they had to have sitting in trenches from Holland to the Swiss border and along the Russian border. They could no longer buy the food they needed, they could not grow more, and they were stuck in trenches and could not displace the British and French. The US did do a lot to end the war with its additional troops, no doubt, but they also had maintained diplomatic contact with Germany during the war and had the contacts and trust to be able to get the combatants to the table to discuss terms of an armisitice. Arguing over who won and who lost the war was the seed that started the next war.
The "War To End All Wars" started 98 years ago. It ended 94 years ago. And you are still arguing about which rifle is best, as if the rifle won or lost the war?