Cant really help on choosing a tree for your garden as i have never planted an ornamental tree in my gatden, in fact apart from 8 large old and rather scruffy pine trees at the top of the garden it doesnt have an ornamental tree in it. I stress ornamental as i have recently planted 2 apples against a fence to train as espaliers. These are the first trees i have ever planted in the garden.
I would though love to have at least one, and have over the years chosen favorites that i would like to plant. this has varied greatly, depending on what trees I had seen or heard about at the time. One has remained constant and that is the crab apple. I like it because it has more than one season of interest; blossom in spring, fruits and foliage colour in autumn and a nice winter structure. Other favorites are silver birch, larger acers, sorbus (rowan or mountan ash) and liquidambar. Not a great fan of cherries, I think thr blossom of many of them are a bit OTT.