Heavens forbid we create a Fantasy world without Frodo, Bilbo, Merry and Pippin. And of course, Sam, let's not forget Samwise.
Halflings vs. Gnomes
If you're considering a Halfling PC you're also looking at Gnomes and vice versa. So what's the difference?
I suppose the relevant Stats are these: Halflings get a +2 to Dexterity while Gnomes get a +2 to Constitution. For Halflings the focus on Dexterity carry over to 'sure-footed' abilities that make them even better sneak attackers than Gnomes; and Gnomes are already excellent sneak attackers. How about a whole party of Halflings and Gnomes? That way you don't really skirmish with you're enemies. One moment they're all standing there the next moment they're all just dead with knives sticking out. Too bad we don't have a Ninja class or do we?
Against Halfling sure-footedness would be the Gnomes' inherent resistance to magic.
Because Halflings don't come from the fey world, they're more grounded and less weird than Gnomes. Also less visually striking but just as cheery.
The Halfling PC
I don't much like the Rulebooks focus on Halflings being slaves and all that (the Rulebook gets depressing when talking about Halflings, Half-Orcs and Half-Elves). I'd rather take my Halfling lore from the Hobbit lore fo Lord of the Rings. Living in peaceful Shire-like communities. Lovers of home and good food.
And that's were Pathfinder and LOTR differ. In Pathfinder Halflings are the adventurous sort. It follows that they would be common among Pathfinder parties. In LOTR Gandalf and the Dwarves nearly had to use a crowbar to get Bilbo out of the house.
Straight on advise: If you're going to be a Rogue, be a Halfling Rogue.