The RHS undertook a trial of Leeks to consider the Award of Garden merit. The trial was Autumn and Early Winter 2015-2016 and in Autumn 2017, the results were published. They rated plants for vigour, leaf habit, colour and disease, the principle culprit here being Leek rust. The leeks were lifted and reviewed with a result that 10 leeks have the RHS award, of which two re reconfirmed. All have hardiness rating of H4 or H5 .
Those which did well in the trial and recommended are: 'Belton', 'Cairngorm' described as more like a show leek which sounds impressive; 'Krypton' 'Portbella', and 'Runner'. Reconfirmed in their status as were 'Jolant' and 'Oarsman'
I usually grow the widely available Mussleburgh with good results illustrated above.