Well mine did fantastic!

I used huge clay looking containers I bought at AJ Wrights on sale for 12 dollars. They can be very beautiful.

I also used a 5.1.1 mix since I only planned on growing them for one season.

When you mean a flower to compliment, are you asking for an annual?

If you're only growing annuals in them, I don't think it matters much whether you use unglazed clay pots, or pots made of plastic or other non-permeable material. To me, it's the medium that's more important.

I prefer the unglazed clay, myself... for both its aesthetic appeal and its permeable nature... but I use terra cotta pots mainly to grow plants that aren't annual, and will need to remain in the pots for longer than a single season.

Terra cotta pots are heavier, and will crack if left out over winter... so you may want to consider where they'll be placed, and whether or not you can store them. And because they breathe, they'll need to be watered more often than plastic pots. Will you be available to water as needed?

For any plant, a terra cotta pot would be healthier, in my opinion... but there are variables to consider.

As for companion plants... you're really not locked into annuals. You could go with perennials just as easily. I'd plant whatever strikes your fancy. I like to mix annuals and perennials for seasonal plantings.

You could use any sun loving annual or perennial along with Geraniums, and today's choices at most garden centers are quite varied. Ornamental grasses, vining plants... the sky's the limit.

Some years I go with the standard mix of Geraniums, a Spike plant, and a few trailers... and other years I opt for a more eye catching mix of annuals and perennials, such as Daylilies, Sweet Potato vines, Petunias, an Ornamental grass... this year I'm thinking of going with Alocacia for my large patio pots.