KL has a new Y+ product, one of the best in the skies. Seat is comfortable and features a footrest. Only available in their B789/10 aircraft in a 2-3-2 lay out. The rest of the doesn’t have a Y+ product but B772/W aircraft will be retrofitted the coming year. Good food, much upgraded compared to Y.
AF has an old Y+ product in their B772/W and B789 fleet with some B77W being retrofitted with their newest Y+ product. This old product is truly terrible. The seat is in a fixed shell and doesn’t recline, only the bottom of the seat slides forward to simulate recline. The result is a terrible comfort for your back and it’s so bad I prefer a regular Y seat. Their A350 aircraft has a reclining newer seat but I haven’t tried it yet. The food in AF Y+ is also terrible compared to KL. AF Y+ food is essentially the same as in Y, with small differences like drinking your beverage from a real glass rather than a paper cup. But the food is the same level as Y, while KL Y+ food is leaning towards J quality and a big step from Y.

So all in all, KL is the best option. You can also consider DL which has a similar product as KL across all their aircraft. Food is also much better in Y+.