The smaller courgettes, round or long, are picked, the better they taste as there is a greater proportion of dry matter to water. I'd pick them as small as hen's egg size, or a cricket ball size maximum.
The more you pick, the more fruit the plant will produce as well.
Slice into 'chip' size pieces and steam for a couple of minutes sprinkled with fresh garlic, and serve with melted butter. Deliiiiicious!

Thank you for your answer ie round courgettes.I let them grow to the sise of a jaffa orange,they tasted very good in a pasta dish.I will pick them smaller next time,thanks again.

Alun 27 Jun. 2010

It's all down to personal taste in the end. Some people like marrow, though I've never understood why! Have you tried the little scallop 'patty pan' squash like 'Green Tint'? These produce lots of little lime green flat fruit, and you can get yellow ones as well.