The Ilex or holly family are perfectly happy to be trimmed and shaped into all sorts of topiary. They are a little more work to train than some common topiary plants. If a more formal look is required the crenata or Japanese box holly forms are much neater in habit, but if it's the big glossy leaves, berries or spiky foliage you prefer, then use the more tradition English hollies. Plant them in well drained, fertile soil and keep them from drying out in the first growing season. Like most evergreens, they do not like cold wet soil. If you have issues with drainage, sort it before you buy any.