A list of parameters I use to test pianos:https://www.pianostreet.com/smf/index.php?topic=27871.msg322628#msg322628
Personally, I like the Kawai tone for romantic and impressionist music. The sound which is rich in overtones is capable of producing a vivid colour palette suitable for this music. Tone is weighted more towards body than attack, and this beneficial when you don't want to hear the clickity-clack of every single note. As for the Yamaha tone, I feel it is quite suitable for music that asks for clarity or a more edgy sound. There is more presence in the attack, and decays are quicker. Less emphasis in the presence of overtones within the body creates a certain clarity or directness of tone. It is wonderful when you don't want to be distracted by overly opulent harmonics in the tone. I have encountered many U1's in schools and institutions, and have found that many of them could be greatly improved with voicing. To me, the default U1 tone is rather bland and average. That is not to say they are a bad piano, just that the sound they come out of the factory with can be much improved with a little tweaking.
Regarding your search, it is important to pick a piano that speaks to you. Narrowing down to a model is only a step. One YUS1, may be completely different to another YUS1. When you finally come across that piano, you will have a sense there is something special about it. It seems there is something that attracted you to that particular U1 even if it was outside your search parameters. Don't ignore such occurrences. They may lead you to discover a piano you didn't know you would like.