Havel's Greatshield. Never fails to block anything
It's hilarious when I show up in a world wearing full gold hemmed with havels shield and a manserpent greatsword. They always try to circle behind me and never fail to get smacked by the horizontal sweep of the MSGS. I've won against several gank squads due in part to this shield.
Grass Crest Shield- I always pick this up before going through the undead parish to fight the boss there. Stamina regen is a big help. But I will change from Grass Crest to others depending on which boss I'm fighting.
Never really use anything other than Grass Crest Shield, Crest shield, Eagle Shield and Dragon Crest Shield.Oh, and I always switch to bloodshield for a certain boss later on in the game *tries to avoid spoilers*.
In PvE i mostly use the Grass Crest. Crest Shield for certain boss-fights, and the Silver Knight Shield for the hard hitters. Used to go with the Black Knight, but the Silver Knight is both lighter and have more stability. The only time I miss it is for the Gwyn fight due to its fire resistance.