Best broccoli/calabrese varieties

Another variable on my seed list for this year is broccoli/calabrese. I haven't grown these before but this year I have bed room to do it so I want to experiment a bit with them. For two of us I was planning on 3 or 4 plants each of autumn cropping and winter/spring cropping varieties. Given the choice, I'd rather have a nice big central head than lots of little shoots, and I'd prefer green rather than red.

Can anyone suggest good varieties for me to try? Obviously they need to be something that's going to be fairly easy to do, since they're new to me. My soil is fairly heavy clay, though the bed has had plenty of compost on it (but not manure).

heavy clay is fine 

For big heads, look for calabrese - broccoli tend to be the "shoots" that you refer.  A couple of years ago I was given some spare calabrese plants called "Olympia" - they are more of a summer cropping than autumn/winter, but they were gorgeous.

Why not try a romanesco type broccoli?  They are the bright lime green (or other colour) heads that look more a weird cauliflower head than broccoli.

Thanks for that. Isn't calabrese all autumn cropping though? If I want to have some for overwintering, I was thinking those would have to be broccoli. I've never eaten romanesco broccoli. Do they taste and cook like normal broccoli or not?

Broccoli tend to be from early spring to summer, calabrese from summer to late autumn but there is a bit of a cross over depending on the variety.  My only experience is Olympia see http://www.johnsons-seeds.com/seeds-plants-gardening/12995/broccoli-calabrese-olympia-f1 which crops from June-October (mine were definitely ready in July)

Romanesco tastes just like broccoli but looks like a strange (and mine were a bright lime green colour) cauliflower shaped head http://www.johnsons-seeds.com/seeds-plants-gardening/16706/cauliflower-romanesco   I don't like cauliflower so I grew it and cooked it with trepidation only to be pleasantly surprised - I would definitely grow it again   

all brassicas get savaged by cabbage white caterpillars!!!  Broccoli varieties seem to be exceptionally vulnerable (my broccoli get targetted first) so definitely grow under fine netting!