First you need to define "best". Do you mean hardiest? Arguably Osteospermum jucundum. Best colour? That's totally a matter of taste and opinion, and fashion, surroundings, and what else you are growing nearby. The most prolific flowers? That depends on where you grow it - it's best in full sun. Perhaps you mean the ones with the fanciest flower form? Whirligig, for instance has spoon shaped petals, which makes an interesting flower, but it needs to go indoors for the winter. As with Fuchsias, the fancier and further "developed" from the species, the less hardy the plant is likely to be.

And none of them is fully hardy!

I treat them as annuals.

The three or four selected shades of O. jucundum are hardier than many people think with a clump in my garden surviving last winter well. They have a flat almost prostrate stem and leaf with very long stalked flowers that stand well above the foliage, quite different from the the bushy types that are used in bedding that certainly are not hardy.

I've had osteospermum Jacundrum outdoors all year around for 15 years and they all survived last years hard winter.

Goodness AMan, I live in the Southeast and I have never kept one through a winter yet - the frosts gets them. Because they grew so well in the spring I never bother to over winter them and treat as annuals.

I'm sure we can't be talking about the same osteospermum DRC

I took cuttings and gave them to my mum who lives on a very exposed hillside in Yorkshire and they survive very happily outdoors all year around even in that position.

I've even overwintered cuttings in small pots outdoors( a few losses but most came through stunted but OK)

This is the specific plant at my mum's house

http://www.flickr.com/photos/31559373@N00/160221777/

If you send me a private message with your home address I'd be happy to send you some rooted cuttings

While there are several good varieties of Osteospermum probably the most reliable is the actual species 'Jucundum'? Which is the one of the ones I grow and sadly I have never kept one over the winter in the garden. They are tender and the advice is to over winter indoors, so I guess you must be lucky with yours? What's your secret?

Yes Anchorman, that is the species I have and it is really very hardy.

I think many people are confusing the other types that have a different growth habit and short stalked flowers which are not hardy in the slightest. Osteospermum jucundum grows almost flat forming a mat of overlapping stems. It throws up single flower heads en-mass on very long stems high above the foliage, quite unlike the other types which die in winter outdoors.

Here is mine on one of my Flickr accounts.

http://www.flickr.com/photos/9008487@N06/2501667861

"They are tender and the advice is to over winter indoors, so I guess you must be lucky with yours? What's your secret?"

No secret. I really do think we are talking about different cultivars. The osteospermum in my garden is as tough as virtually any plant I know. Most osteo's are tender. The one I have isn't.