Answer: Your planter should be as large as possible and reflect the architecture of the house. It could be wood or metal painted to match the trim, or if concrete, be left to age naturally.
The most formal look is provided by clipped evergreens sentinel style. Another alternative would be to do a simple evergreen foliage treatment of vining English ivy (Hedera helix) which would soften the look of the entry. For color you can add seasonal flowers if desired, but only if there is someone who will care for them on a daily basis.
Whichever plants you use, keep in mind that they will need regular watering, feeding, and grooming. Since container growing is stressful on plants, you will probably also need to replace them periodically. Your local nursery should be able to make more specific suggestions as to what would do best in the lighting available, meaning sun or shade, and taking into account any other special conditions of the site.
Make sure, also, that there is enough room for safe foot traffic between the planter(s), door, steps, sidewalk, curb, and so on. Larger planters are easier to keep watered during the summer and also provide better insulation for the plant roots during the winter. This volume difference can be critical to the plants' chances of survival or failure, as well as in their overall healthy appearance during the growing season.
I would caution you that a planter is all too often unfortunately an invitation to vandals, litter, cigarette butts, dogs lifting the leg and so on. For that reason, especially if this is a busy street situation, you might be happier in the long run with something as simple as an attractively designed sign bolted over the blank wall space. That would look good year round with no more effort on your part than an occasional washing.
I hope this helps with your planning.
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