Assumption: your squirrels have the same hands and roughly the same body that earth squirrels have.
In order to choose a weapon, it is important to know (and I keep repeating myself there everytime I answer a weapon related question): what are the conditions they are used in? What opponent do you have? What armor do they wear?
First off, squirrels do have kind of opposable thumbs, but they don't use them the way we do. But I think that if your squirrels are of higher intelligence, they may use them or quickly develop them to full effect. Since opposable thumbs are a huge evolutionary advantage, especially for an intelligent being, I assume your squirrels have them.
Squirrels hunting prey
If your squirrel is hunting other animals, for example to gather fur, leather, bones, sinews fat etc., they require typical hunting weapons. I doubt a squirrel can possibly generate enough kinetic energy to seriously injure bigger creatures like deer or bears. Even wild boars will be a no-go. But they could kill smaller prey like bunnies or mice. For that, they'd either go trapping, or hunting with small bow+arrow or by flushing them out of their burrows. Since none of these animals can fight back efficiently, I think smaller weapons like axes and knives (flintknapped?) would do. They also allow the bearer to enter tight burrows, where a long spear would be a hindrance.
Squirrels defending against predators
In order to defend against a predator, you need to do one thing: don't get eaten. How do you not get eaten? Especially if you are a frail little squirrel? You stay the heck out of reach. So all our defensive weapons will be long and of long range. But, even with a long spear, a squirrel probably can't defend against a cat or a wolf. The animals are just too huge, and if you don't hit a vital point (eye, nose), their first attack will kill or maim you. Even if you do hit an eye with your spear and somehow kill a pouncing wolf, the heavy body might still crush you. So melee weapons are completely out. Also, while holding a weapon, you can't climb. And fleeing is probably the best you can do.
So, vs. predators my best guess would be: escape to a tree, warn your friends. While the predator chases you, your friends make ready. If you reach safety on top of a tree, all is good. But if the predator tries to chase you or corners you, your friends need to help. And I think only ranged weapons can help you here. And especially the sling might be super useful here. Slings can be made from cloth, and are therefore easy to store and carry while climbing. You can always have a sling with you for self defense, while a bow is a hinrance, and takes longer to make ready (you can't always have a string on your bow). Guards might go for bows or throwing spears (if thrown down from a tree, they might develop some power), but the common squirrel will carry a sling. This way you might chase predators off your tree.
The main cities and outposts will probably be secured by walls of spikes pointing down the tree trunk, making it harder to climb it for bigger creatures. In these stationary locations, your squirrels might also store huge nets, that they could throw down on climbing intruders, catching them and potentially killing them during the fall.
Squirrels fighting squirrels
Since squirrels are fast and agile, but rather weak, I assume they do not wear significant armor. Maybe an occasional chestplate made from bark, since bark is relatively lightweight. If fighting another squirrel, you'll need to keep a balance between mobility and armament. If you use your hands for fighting, you can't run and climb. So I think one-handed weapons will prevail. And against unarmored opponents, weapons like the rapier and light sabres proved most effective in our history. A rapier could be made out of cactus spikes or even wood, if you don't have metalworking. Sabres could actually be flintknapped as a whole. Or you could make swords like the macuahuitl, that would be rather heavy and probably one-and-a-half-handed, but a hit will END every squirrel.
Or go for the lulz
If technology is not that much of a thing, and you just want to go for the funny ideas, try exploding nuts (thrown with slings), hand crossbows, flintlock pistols, or, most importantly: spears with detonating tips, used by squirrels with impressive mustaches, that ride on giant ferrets, while wearing Pickelhauben, monocles and speaking with a german accent...