what's everyones favorite reward?

Always welcome! Sorry but my Sim is using your shower & stove :D

Carefree and Shameless. Carefree meant your sim never got tense. It used to stave off the Island Living debuffs, but some of those have been changed to scared. Shameless basically yeets the embarrassed emotion completely, meaning no more Embarrassment deaths.

Observant.
I want to know everyone's personalities, without the work. That way I know who to befriend and invite to parties. Who wants an evil at their toddler's birthday? Who wants a good at an evil scientist's retirement?

Always Welcome.
This one is second. Sims should be able to grab a snack at their parents' or fiancée's houses.

There are many good rewards depending on the character, but I'd have to say in general:

-Carefree
-Shameless
-Seldom Sleepy

as my top 3 favs

Depending on what you mean though, the "small" ones,

-Incredibly Friendly
-Always Welcome
-Observant

(I don't use the "big" ones much since it takes away from gameplay, I find.
Other than:

-Brave

EDIT: Depends on the characters and the situation they are in. ;)

Favorite reward? Probably the Mentor trait.

Top three I get asap - Storm Chaser, Waterproof, and Observant. Frequently followed by cold and heat resistance (never immunity) Others vary depending on the character.

Depends, for practical reasons, I like the waterproof, always welcome and observant ones. For skill building, I like the morning sim and night owl ones because it gives a boost. If I have to pick just one I just enjoy the most for no reason, it is maybe the iceproof one. I really like the moodlets they get during winter and snow storms.

Storm Chaser. Makes no sense that all sims go into a frenzy when a thunderstorm occurs. Also, I love storms.

I don't like to use the reward traits to make the game easier, but I like to use them more as "additional personality" traits.

For example, an outdoorsy and adventurous Sim would have Storm Chaser. Or maybe a genius and perfectionist Sim would have Observant.

Always Welcome is a great and useful reward trait, but I've opted to use Bienchen's morewelcome mod for my own playstyle.

I like Marketable and Creative Visionary for creative Sims who might want to try to make a living through their hobbies.

Another trait I really like is Great Storyteller. I usually give it to Sims who I find charismatic and always seem to have some amazing story to share. It can be useful in gameplay to change someone's emotion. When my Sims throw a party and someone comes over angry, my Sim can share a Dramatic/Engaging/Funny/Outrageous/Unbelievable (if they're confident) Story and change their emotion...you know, so they stop kicking my trash can and yelling at everyone at the party. Just be careful with Funny and Outrageous Stories as they can kill Sims if they make them too playful.

Always Welcome so it's easier to visit friends and relatives.

Shameless because I hate the idle animation for embarassed sims. Also, I already have a mental reel of embarassing moments of my own, thank you.