I would say Saphira or Angela. Angela is just a very interesting character & a lot of interesting facets of her life are dangled in your face & then snatched away. Saphira I like more than Eragon because of her wisdom &, despite being a supposedly self-indulgent dragon who thinks herself the most beautiful in the world, does not outwardly display some of the arrogance Eragon does.
I feel like Arya didn’t get much character development, relative to everyone else. She’s the same withdrawn person throughout the entire books, & only near the end she’s like “oh I would be ok with pursuing a relationship” just seemingly at random, purely because Galbatorix is dead, & then of course never actually ended hooking up lol.
Nasuada is awesome. She’s not a very exciting character, but she really has depth & will, changing a lot & going through hell to get where she ended up. Not my favorite character, but definitely respectable.
Brom the Storyteller is my favorite beacuse I feel like i relate to him a lot in life lol :) and I really admire Brom as a character and feel like his story isn't done yet. For intstance his earlier life and how he became a Dragon Rider and the seven words he spoke to Eragon before he died.