The best machine is the one that has all the features you need, and you feel most comfortable using. I have 2 earlier Brothers and love them both, but the pre-owned Pfaff CV I bought last year has one great feature positioning embroideries that I don't think other machines have, so will keep it for that alone.
I watched several youtube videos on all three on your list. Couldn't find much info on the Janome, which is a shame, as I love the easy pop-up needle plate (no screws to battle with) It only takes up half the width due to the embroidery arm fitting on the back, and I like their dual-feed foot. The Dream and Destiny machines seem to have a lot more features, and similar. I think they are the same machine, made by different companies.
If it were me, I would spend a few hours (maybe not all at once) at the dealers' having thorough demonstrations on all of them.
Do let us know what you end up with.