This can basically turn into a Ford vs. Chevy, John Deere vs. Kubota type question. Most of my personal welding machines and our company welding machines are blue (Miller). The exception to this is an old Lincoln Idealarc 250that welds really well.
When I was trying to decide on Ranger (Lincoln) versus Bobcat (Miller) for the farm, I watched all the service trucks going up and down the highway. For the smaller (gas engine) models, I noticed there was about a 5-to-1 ration of Miller's over Lincoln's. The mechanical contractors that come into our plant all use Millers in the gas engine models. I don't know how much of a conclusion you can draw from this, but it means something that folks relying on their machines for their living were going Miller in this size range. This goes the other way when you get into the diesel machines. They were almost 100% Lincoln SA's.
Dealer service wasn't an issue since the same guy sells both. I bought a Miller Bobcat 250. I don't use it a lot. But, when it needed, it always starts and welds really well. I plan to welding bucket hooks on this afternoon. I started it yesterday for the first time in 2 or 3 months and it fired right up.