I would stay with Tumbling Tom. I don't grow them but if everybody it talking about them, there must be a good reason. Anything that attracts loads of bees would work, salvias, zinnias, sunflowers. Sometimes I'll get a pack of wildflower seed mix and sprinkle them 'here and there'.

The Telegraph newspaper did a test a while back. Here's their verdicts (the number is marks out of five based on flavour):
Hundreds & Thousands 4/5
Tumbler 4/5
Maskotka 4/5
Garden Pearl 3/5
Tumbling Tom yellow & red 3/5
I had to refer to my notes but just search 'toms, hanging baskets, Telegraph' & the original article should be easy to find. There were some other compact plants that were upright but would fit baskets too

I would go for the biggest basket you can find. 16 to 18 inches at least. I would also put just one plant in a basket without any companion planting. Otherwise you will be forever watering it. Perhaps a plastic saucer in the bottom.

Thanks that's brilliant of you all.
I am always suspicious of newspaper articles as they are often linked to a grower/seed supplier. That's why I was asking you goyers as I know some will have grown them.
they have 12/15 " baskets already so I doubt they will want to buy more and I thought just the one plant. I'm not going to be the one watering them so I don't care ;o)