I don't know why my favorite beers have always been bitter and strong.  I love Guinness Stout more than any other type of beer.  I hear that people ask why the Guinness tastes so nasty, and you could practically eat it, it is so thick.  The truth is that the bittery flavor just comes from the hops.  Guinness is made of water, hops, barley, brewers yeast and isinglass finings (fish bladder with collagen which clarifies wine and beer, and is unlikely to remain the finished product), and lst it is pasteurized and filtered.  The reason that the beer is so dark is for roasting the barley, which also adds flavor. 

Another type of beer I like is Black & Tan, which is mixing stout with porter.  Porter Basically just includes dark malt, but other beer varieties include honey, vanilla, pumpkin and bourbon. Black & Tan still has great flavoring, but Stout is my fave.  A new type of beer which is like Guinness, is B.J.'s Brewery which has Tatonka Stout, and another type which I have heard about, but have never been there, is the Oatmeal stout at Four Peaks (which is a college bar/brewery and grill in Tempe).  I have been waiting for a while to try different beers at Four Peaks.  They have a great item that sounds tasty called the "Stoutamisu" which is tiramisu with espresso sponge cake and ladyfingers that are layered with Oatmeal Stout.  Personally, that sounds pretty awesome which I will get a chance to try.