Okay, I'm going to rant now.
What the hell is the logic behind Favored Enemy? Apparently, you've studied your enemy very well, so you're really good at dealing with him. Let's examine the bonuses you get. Bonuses to Spot and Listen, to damage rolls, to Sense Motive, to tracking, and a few others.
So . . . I've studied Goblins. I know where a Goblin's body can be hurt most easily; I know what they sound like as they walk, and I can recognize their facial features and gestures well enough so as not to get caught off guard by them. If I run into an Orc, I don't get this benefit, because Orcs and Goblins are very different.
Next, for my next favored enemy, I've studied Humans. I know how to injure a human by going for the weak spots like the third vertebra, and I'm familiar with the common aspects in human sociology to let me tell when a human is telling a lie, whether that human is a tall, hulking Nordic man or a skinny teenaged Japanese girl, each from vastly different cultures. But if I try to tell if an Elf is bluffing, or if I want to hurt an Elf, I'm out of luck. His gestures and anatomy are just too different from humans. Heaven forbid I want to hurt a dark Elf.
For my third favored enemy, I choose Aberrations. In an adventure, I come across a room filled with an Aboleth, a Mind Flayer, a Beholder, and a Carrion Crawler. I am not worried. Because of my superior knowledge of anatomy, I can discern the shared weak spots of these three monsters, despite their completely different body plans and minds. Of course, I can't possibly know how to hurt a Frost Wurm. After all, it's a magical beast. It's far too unrelated.
No, I'm sorry. The explanation in the PHB is stupid and lame. The only possible explanation my group can accept for these ridiculous bonuses to completely arbitrary groups is that rangers hate these monsters. They do not derive benefits to combat and hunting because of close study, but rather because they are racists.
Durned racist rangers, hating on everybody.
I'm going to make a ranger PC with Favored Enemy (Playas).