There are far too many different styles of beer that are too different to select just one overall. Here are some faves:
If you have never tried it, try Fuller's ESB. It is one of the smoothest beers in the world. This is obviously my pick for an ESB.
For a brown ale, Samuel Smith's Nut Brown. They also make an excellent IPA.
For a stout, try Murphy's as an alternative to Guinness. A nice dessert beer is Young's Chocolate Stout, too.
For a Belgian style white, Celis White.
For an old ale, Anchor's Old Foghorn. Don't drink more than one if you are driving. Anchor also makes an excellent porter.