The great thing about raised beds is that you can put really great soil in them, which means that you can choose from an enormous array of plants.
I would choose a style that you like, and get things around that theme. In a city garden, where space is very limited and you need something to be of interest year round, I would make sure I have something with interesting foliage of some sort, which will still look good when there aren't so many flowers. I would choose one or two evergreens with foliage you like to provide that. Maybe something with reddish leaves.
Not that many things flower for a very long season, so the best thing is to plan for a succession of blooms if you want flowers all year. You don't have that much space, so I wouldn't get overly obsessed with that, or you might end up with something where there is one tiny bit blooming at any one time, with the rest not looking that great. Choose plants with many seasons of interest, rather than just when they are in bloom. Think of the colours of the leaves in autumn, or the stems in winter, for example.
Bulbs are a great way of cramming flowers and colour without taking up too much space. You can plant them in between perennials or other plants that then cover up the gaps they leave when they die down.
Another thing which may make sense is to put in a small tree in one of them. It can grow above the fence, breaking the line of the fence and providing a difference in heights, and you can plant underneath it. I love japanese maples for this kind of thing.