In March, I flew United International Business from London to Washington and then took the Cardinal to Chicago and the CZ to San Francisco.
The best food by far was on United, in terms of quality, quantity and service. It was also better than BA business on the way back to London.
The food on the Cardinal was probably equivalent to airline Economy food. The CZ was better but not a patch on United.
In my experience United international Business First food service is categorically better than Amtrak Sleeper food in quality, quantity, variety and presentation, though IMHO they could add a 5th entree choice to make it even better. Of course booze is free on United and not on Amtrak, and there is absolutely no haggling about how many cans of soft drink can be had, well of course can is an undefined term there, you get it in real glassware. The clear additional things are the nuts, appetizer and of course the ice cream sundae prepared with your favorite topping right in front of you, plus the fruit and cheese with after dinner drinks. And throughout the meal you can get as much bread of five different varieties as you wish.
On the longer flights I also like the midflight sandwich, dessert, cheese and fruits buffet that is laid out for anyone to use whenever they want.
In international Coach food is adequate, probably at par with Amtrak diner, though overall quantity is perhaps a little less. It is a pre-plated meal served in a single shot on a tray, unlike in BF, where each stage of the menu is served separately, using a dinner setting on tablecloth, and real thick cloth napkin and heavy silverware (three sets of fork and knife and two spoons) are provided. One nice touch is that the cloth napkin has a buttonhole in one corner so that you can hang it off of your shirt to protect it while you are eating.
I guess I will get to experience the enhanced international Coach fare in June on my business trip to Berlin, unless I manage to wangle an upgrade. The Newark - Tegel flight this summer is an international 767-300. I will be happy to report back after that.
Frankly, United hit rock bottom immediately following the merger. Since then they have been improving in measured steps. They still have ways to go before they become anything like the East Asian airlines though. They should be caught up with most Europeans pretty soon and are probably better than some already.
While Amtrak is downgrading the dining options on the Silver Star, United Airlines (gosh I hate even typing that name!) has announced upgraded meal service for economy passengers on long-haul international flights.
Starting June 1, economy passengers will now receive three-course meals and free beer and wine.
Here's a link to their press release which includes menus:
http://www.prnewswire.com/news-releases/united-continues-upgrades-with-new-international-economy-meals-complimentary-beer-and-wine-300066355.html
Any upgrade is still 10000% inferior to Amtrak's downgraded meal options.
Wait! Since when does Amtrak provide free food in Coach? So clearly even without upgrade the food in international Economy is better since any food is better than no food.
The thing that Amtrak Coach passengers have going for them is that they can buy meals in the Diner. The United Economy food is better than the fare one gets in Amtrak Cafe in my experience.
IMHO the Amtrak Diner fare was slightly better than the pre-upgrade food in international Economy. After the upgrade United will probably be better in terms of what is available in the package, though not in terms of variety of entree yet.