Halfling. This is the weakest race. No good for any role.
Being small race with -2 str, no-good for any melee class. This is not just because they inflict low damages. Many monsters have improved grapple and low-str melee combatant are eaten (or constricted) very easily.
Not that good as an archer either. Though has slightly better attack bonus, low damage still sucks.
As a cleric, dex bonus does not help much as they wear full-plate. And small weapon and low str still suck.
As an arcane caster, races with high con and low-light or darkvision are far much better.
As a druid, maybe not so bad. But races with high con and low-light or darkvision are still much better.
Meant to be a rogue race. But slow speed is no-good for a flanker, especially with new tumble rule (only 10 ft.!). Also, the only demi-human race which has normal vision. Races with low-light vision or Dark Vision are much better as scouts. And, Dwarf Rogues and Elven Rogues are much better as "finder".
Well, lets say some comments on other races.
Dwarves ... The strongest I say. Tons of abilities. Good for any classes which does not need CHA. Even with low speed, not so bad as a rogue thanks to their Stone Cunning ability.
Elves ... -2 Con sucks. But still make a good rogue. And not that bad as a ranger.
Gnome ... makes really good arcane caster. High Con and low-light vision. That's said.
Half-Orc ... is the only core race which has str bonus and thus good for melee types. Darkvision is still a great ability. Also, surprisingly good as a monk or a druid.
Half-Elf is ... an alternative to human. Some combination of classes can be practical only for those 2 races because of favored class rule. And Half-Elf's racial traits (especially low-light vision) are often good substitute for additional feat and skills. And, with new bonuses for CHA based skills, HE character can be a very good negotiator. Good for paladin, sorcerer, bard and such.
Human ... is often the best choice when you don't want any demi-human traits. And sometimes human and half-elf are the only choice whey you multiclass in some combination. Additional feat and skill points are always good at least. And, in most settings, human fill the majority. That is important when you need someone who can hide into clouds, or someone who can be easily trusted by people.