As a profession, an advantage which garden design enjoys, compared to landscape architecture, is that everyone knows what is involved: design skill + garden knowledge. The disadvantage from which garden design suffers is that too much work has been done by people with far more garden knowledge than design talent. As the name should always remind us, it is necessary to have both. There is also a tendency for garden design firms to have their roots in the construction business. The truth of the matter was put by Hassan Fathy, writing about architecture: the making of a good garden requires a partnership between the client, the builder and the designer. If one person has all these abilities, fine. If they don't, help is necessary. For example, if you are the client and gardener, employ a design consultant. If you are the client and designer, employ a garden maker. And if you are the designer and builder, you must draw a client into the design process.
No country can surpass Italy for its renaissance gardens, France for its Baroque gardens England for its Romantic gardens or the Americas for their Abstract Modern gardens (though few are open to the public). Nor can anyone know where the best twenty-first century gardens will be made. Its up to you.
There are many ways of creating a beautiful garden. No one is better than another: they suit different people.
If you simply want a lawn, rose beds and a rockery, all you need do is look at a few neighbour's gardens and do what they have done. Many un-designed gardens are loved and beautiful. Others are not.
'Cottage gardens' can also be un-designed in the sense of resulting from a set of careful decisions about functions - and a traditional delight in good craftsmanship.
Garden with sun dial
Garden design plan
Chateau Villandry, France