Between the three you really don't have a lot of important differences.

Barbarians get slam but they pay a 5% XP penalty for it and it gets less useful as you level up since you will never gain skill in it. Barbarians are also nightblind so you will need a light source until you get a buff or item to fix that later.

Vah Shir get safe fall and sneak and pay no XP penalty. Neither skill is game changing but both can be handy. I really notice missing all the bumps when I play a cat rather than something else. Sneak is useful for shopping form some merchants who don't like you and can help with some quests.

I know very little about the frogs so I can't help you much with them.

The most common answer you will get to this question is "Play what you like". No racial abilities are that overwhelming enough to make it fun playing a character you hate.

I play a barbarian, and nightvision never been any problem for me. You get that kobold necklace in tutorial, and then you just go kill a fire beetle for a fire beetle eye. Actually, I got 2 of them for a long time, one in a bag and one in a inventory slot. I got a friend with rez, so if she couldn't rez me right then I would loot my corpse, leaving that fire beetle eye on corpse until rezzed. Everfrost is also a very useful hunting ground. You will get good at swimming too.

The best with barbarian is being able to slam. No, you don't gain skill in it, but hey, it interrupts spells. Very useful still at higher lvls at those casting mobs. I use that a lot. It's not nice to have a dragon that gates only to come back with all his friends - but you can't slam in bearform :-(

I would love to have iksar regen, but I don't want to look like one :-)

Cat sneak would be nice, for safe fall I use levi anyway, but could been useful at lower levels. And cat city is soo nice.

Frogs, same as iksar, don't want to look like a froggy.

Shammy is a wonderful class, but race is not that important. Choose the one you like best