One of the things that affects how powerful companions are is the player's Charisma. Charisma affects Companion Nerve from +5 at CHA1 to +50 at CHA10. That's the bonus to Armor and Damage inflicted by a Companion. I always go for high Charisma so they'll be strong and for the speech checks.
Most recently I was completely impressed by Rex and I wasn't before. He would sit down and I'd have to keep going back to find him. This last experience was that he was awesome. He had high health at my higher level and fought like a beast.
He actually went over the side of the dam when leaping for a Legionairy and I thought he was gone but he found his way back and fought to the end. He takes enemies down alone most of the time. Raul is incredible because his Guns skill is so high and Arcade is fearless, often leading the way towards the enemy to take it out.
I'd have to say Lily is probably underrated by me, unfortunately, but I haven't used her enough. She hit me with her weapon last time and that put me off.
I'll use her again though.
:fallout: