My favourites are Balin and Dwalin and I am really divided to.decide which one I like more! :-)
I love Dwalin cuz he is the pure Example for Dwarven Warrior and Might in Battle a professional Soldier with amazing fighting skills loyalty and yet somehow wise in his own way! :-)
While Balin is excellent and skilful Warrior to who has great Wisdom and cam give irreplaceable advice in every kind of situation and is a Lord of Noble Statue ! :-)
So I will go with Dwalin slightly a above Balin! :-)
After them ia Fili and after him Kili! :-)
But my favourite will be Dwalin especially in his bad ass Erebor Heavy Armor! :-)
P.S.I think you should remove Thorin from the Poll cuz we are talking about Favorite Companion of Thorin and he can't be his Companion well except if he is not like Gollum!