The beef sold in delis is usually slice topside or siverside. I have never seen brisket, which is the slow cooked joint. When cooked it breaks up into shreds. Tasty, though.
you could try fillet steak, it's the tenderest but not cheap. (Also, it has less flavour than the tougher, fattier stuff.) M&S and Waitrose are doing good ones these days.