I am actually in a similar boat myself, but I have not used both. They have the same Snapdragon installed I believe, so the speed and functionality should be quite identical if not very similar. But as per usual with flagships, if you want to pay a little more for a better camera, better specs (arguably, as sometimes, these things are a little subjective), then go for the U11. However, the OP is supposed to have great battery life, dash charging, and is snappy and smooth experience-wise.
I personally wanted the U11 when it came out but I can't justify spending that much money on a phone; especially when I see phones like the OnePlus 5 that are arguably just as good and get the job done just as well. It's a tough choice, as they're two great phones. Try watching some unboxing and review videos on YouTube to see which one may better suit your needs.
Let us know what you decide!