Default Choice
Situational
Never

Hunter-Gatherer: This talent helps keep both Rexxar and Misha alive assuming you have been picking up enough Regeneration Globes throughout the game.

Flare: Flare - Can be useful since unlike Far Sight for Rehgar and Clairvoyance for some heroes it has a short cooldown however the duration is shorter. I'd recommend this talent if the enemy team has a Zeratul and/or Nova.

Grizzled Bear: Unlike Hunter-Gatherer only works for Misha which hinder Rexxar's ability to live.

Survivalist Training: Regeneration Globes never gave you that much mana to begin with so Survivalist Training won't make that big of a difference, that and during team fights there won't be any globes around for you to pick up most of the time unless you are fighting for objectives and at lanes but even then it still wouldn't be worth it since you should have good mana control.

Crippling Talons: This can be great against enemy heroes with good mobility which can help you and your team take down fleeing enemy heroes or one that is alone.

Hungry Bear: It can great for Misha to stay alive. I'd recommend this talent if the enemy team isn't very mobile or if misha dies a lot.

Taking Flight: It's not a bad talent per-say but it doesn't beat the utility from Crippling Talons and the keeping Misha alive from Hungry Bear.

Easy Prey: This talent doesn't provide much use against enemy heroes however if you are going for a jungle build you can pick this talent but this build will focus more on Survival and Crowd-Control.

Aspect of the Beast: Allowing Misha to charge even more which can stun enemies more frequently can help destroy the enemy team.

Blood of the Rhino: Adding 5 seconds for Mend Pet can help Misha alive however Mend Pet can already heal for a good amount. I'd recommend this talent if Misha gets focused a lot and you are going to pick Critical Care at level 16.

Throwing Axes: This isn't that bad of a talent but you won't find that big of a difference of Rexxar's range. Besides there's a line between getting too close to Misha when fighting and getting too far from her to help.

Bird of Prey: While this talent is great for waveclear and jungling it's not very useful on team fights.

Bestial Wrath: Bestial Wrath is great for single-target damage and is useful for focusing on a hero. I'd recommend this ultimate if the enemy team is not very mobile.

Unleash the Boars: Unleash the Boars is great for team fights which can be a good opener or good for fleeing heroes. I'd recommend this ultimate if the enemy team is pretty mobile and/or has a Nova and/or Zeratul.

Thrill of the Hunt: Thrill of the Hunt helps what Rexxar and Misha lacks; Mobility which can help save them or catch an enemy hero.

Bear Necessities: This talent can great for moving Misha around a bit if needed and is also useful for catching an enemy hero you want to stun but is out of range and another hero isn't in the way.

Barkskin: This is somewhat similar to Spell Shield except it has a shorter cooldown and is more controllable and even stronger. I'd recommend this talent if there's an enemy Kael'thas, Jaina, Zeratul or any other bursty ability damage dealers.

Wildfire Bear: This isn't a bad talent but the other talents are more useful.

Primal Imtimidation: This talent is great against enemy heroes who have at least 2 basic-attack heroes like Valla, Tychus, Thrall, etc.

Aspect of the Hawk: This talent can be useful on helping you deal more damage especially since you used Spirit Swoop to slow an enemy down and using Misha, Charge to stun it'll be easier for you to keep hitting your target.

Critical Care: The heal on Mend Pet is already pretty strong but if you notice Misha being bursted down quicky then this talent can most likely save Misha from death. I'd recommend this talent if you picked Blood of the Rhino at level 7.

Feign Death: As a warrior your job isn't to avoid getting hit you're supposed to take damage however it's still worth taking if Rexxar keeps dying and since this has a shorter cooldown compared to Ice Block it makes it better. I'd recommend this talent if there's no healer on your team.

Hardened Shield: Hardened Shield will help keep both Rexxar and Misha alive especially if the enemy has a good amount of burst damage.
If you picked Bestial Wrath: I'd take Hardened Shield about 75% of the time.
If you picked Unleash the Boars: I'd take Hardened Shield about 50% of the time.
But overall though it depends on your team and the enemy team's comp that'll have you decide between the three talents.

Spirit Bond: If you picked Bestial Wrath at level 10 and the enemy team doesn't have lots of burst damage then this talent is worth having for allowing Misha to deal more damage and heal Rexxar for half of that damage. I'd recommend this talent if your team lacks and damage and the enemy team lacks burst damage.

Kill Command: The increased damage is nice but rooting the enemy team is the best part about this talent can allow your team to burst them quickly. I'd recommend this talent if the enemy team lacks burst damage and they don't have a Kharazim with Soothing Breeze.

Frenzy of Kalimdor: This is bit of a weaker version of Nexus Blades since it only increases your Basic Attacks' damage by 10% instead of 20% and the slow is unnecessary since you already have Spirit Swoop and Misha, Charge.