I'm probably in the minority, but I always try to fly Business/First Class whenever I go to Europe, which is usually once a year. Delta is my airline of choice, and while I haven't had any luggage issues, they do always change the flights multiple times up until you leave. This gets annoying and, when they change equipment, means you may not get the same seat on the new plane that you had on the last. I have found that I need to check my flight every couple of months to see what changes they have made to the time and equipment(they don't always email you the change).
Because I travel solo, flying Business Class to Europe allows me to have a seat by myself, which I prefer. The first couple of times I flew to Europe was in both regular and economy comfort. The 8+ hours on the plane was excruciating, I never really felt comfortable, and I didn't sleep. Not to mention that the food in coach leaves a lot to be desired. Typically, if I am flying 8 hours or more on one segment, I fly Business class. It was definitely a must when I flew the 15 hours from LAX to SYD! I was actually able to sleep for a couple of hours on the flight. Unfortunately, I haven't found domestic first class to be worth it(other than to Hawaii). The service just isn't the same on the shorter flights. However, the problem is that once you start flying business class, it's hard to go back to coach.