To be honest, my favorite kinds of gardens are a bit wild and unruly looking. My only hard and fast rule is that trees have to fit the house and land space. There's nothing more irritating to me than trying to go inside a single story dwelling and see what's going on only to have a tree in the way at every turn. Because of this I tend to only use tall and/or bulky trees on very large lots where they can be placed out of the way of my field of view while playing. Otherwise, I use a lot of flowers, rocks and bushes/shrubbery and forgo trees.
I like color so I tend to try and fit as many colorful blooms in as possible unless its an ultra modern build in which case I typically stick to greenery, rock gardens and very manicured looking, balanced green space.