What's your pleasure as to type and purpose? Flowers? Annuals, perennials. Bloom together or bloom all year. Or an ever-blooming type, like plumbago? Sweet smellers in the sitting areas? Want to be largely hands-off, or want to fiddle with it regularly?
Want to hide any of that wooden fence with tall plants or vines? Want to attract butterflies or hummingbirds? Want vegetables? Or herbs. Some large herbs next to seating, like rosemary, lets people sitting there brush a hand across the plant and release the aroma.
I think you may already have herbs, maybe rosemary and sage, in the L-shaped area, but they do not look healthy. Rosemary particularly can be a large, dense shrub that can be shaped. It may well be time to improve the soil. Nutrients leach out over time, and fertilizers can leave salts behind. It's not hard. There are many resources online about using good compost and amendments like perlite and virmiculite to create a robust, aerating and well-drained soil.
And how many hours of direct sun does each area get? That is critical to plant choices. I suspect many herbs will do fine in the light on L-shape, but some will get leggy with that much shade, as the sage has done. Is that Maidenhead, UK, or New Jersey?
