First, giving just one data point, I flew TATL last summer, one direction on DL and the other on AF, and I thought DL was better. Foreign airlines have a much better reputation for first, but not necessarily for biz.

As for biz vs. first, I have never flown F, but I think biz is just fine. Quite a few people have posted videos of their overseas F flights, so you might google those. A personal opinion, the biz seats are a little narrow to sleep in, but how much extra do you want to spend for the extra luxury when you're unconscious? Can you sleep as well in your jeans and sweatshirt as you can in their pj's? Sometimes the F lounges can be a nice touch though.

But the time/points ratio is a biggie. My wife goes to Europe every summer, I went with her last summer but I might go one year out of three or four. If that's all we use our points for, we'll have enough points to fly biz forever based on what we earn. I guess if I saved 40K DL points by flying coach I could get a free domestic flight worth maybe $500. So I ask myself how miserable I'd be at the end of a long trip in coach. And my answer is, pretty damn miserable. There are other benefits. When we flew back from Paris last year there was an express checkin line, I think an express security line, lounge access, express line for passport control. And frankly, traveling with your significant other, it's a hell of a lot more romantic.

It's a personal preference. I booked her trip to Europe next year in first. (Unfortunately, on United, not one of the foreign carriers.) It will cost an extra 25,000 FF points, but how many brownie points will it get me?