Arcane and Aberrant for reach and free spells, easily.
Arcane's got to be in the top 3 but the other 2 are arguable. Abyssal for becoming huge? Aberrant for reach and other weirdness? Shadow or shapechanger for their obvious tricks, destined for the numbers, or vestige for semi-martial flexibility?
I might choose arcane, shapechanger, abyssal, but the last 2 would depend on my mood.
I think you can throw Abyssal/Aberrant into the same pile of "get absurd reach" because they can take a turn (Or not at level 11) to cast the other buff to get absurd reach. They are fairly similar, except Aberrant has significantly better defenses while Abyssal has some moderate offensive power built in.
Arcane is flat good, as you just get so many free buff spells. It honestly destroys the action economy and its amazing. Its probably the best if you aren't trying to pull some sort of reach shenanigans.
The third choice is a bit harder, but I have to give it to verdant. It gives you scaling fast healing, a huge AC buff, optional reach, crazy free plant allies, constant thorn body, and the capstone is absurdly powerful basically giving you plant immunities and free tremor sense.
Aberrant can qualify for Aberrant Tumor, which can have the Figment archetype. So you can go around telling people, "It's not a Toomah!"
Figment also pairs well with the Die for your Master feat.
Salamander as an honorable mention for being one of the few (only?) ways to get a tail-slap. It caps off the Tengu Kraken-Caller Druid and Crossblooded Salamander/Aberrant Bloodrager natural attack build.
Destined is worth mentioning for just being tanky as hell. But... its main ability worth keeping is the one that gives luck bonuses to AC/saves, and everything else can be rather safely traded out for rage powers.
...it is the best "this is basically just barbarian, but I switched some thing around and got spells/arcane strike". Which is nice (no one is ever going to say barbarians are not effective at what they do), but people often turn towards blood rager for a different effect.
I think you can throw Abyssal/Aberrant into the same pile of "get absurd reach" because they can take a turn (Or not at level 11) to cast the other buff to get absurd reach. They are fairly similar, except Aberrant has significantly better defenses while Abyssal has some moderate offensive power built in.
Not necessarily. At level 10, blood ragers can free action cast a spell when they blood rage. There are various restrictions... but suffice to say- longarm is an option. You don't necessarily need ALL of the reach boosts all of the time. Grabbing a polearm and adding +10 of reach (from rage power and spell) is enough to allow you to attack enemies at a distance that some slow races cannot reach even after a move action. And that is certainly enough to make you a great circle of pain that practically divides the entire battlefield in half.
I know, I've run an Abyssal Bloodrager up that high. When I raged I naturally became large sized giving me 20ft reach with my Polearm (and 10ft reach with my free claw). With Longarm that could push me to 25ft, and it was often the spell I cast when I started raging. However, it was not the only spell.
Regardless, I had a high dexterity, combat reflexes, and threatened 25ft AoOs with a Large Lucerne Hammer for 3d6+modifiers of pain.
However, my point was that BOTH aberrant and abyssal do the same thing at level 4 which is grant you absurd levels of reach. This is one area where a Bloodrager can make themselves stand out from a barbarian, and they do it in different manners. Abyssal enlarges, while aberrant long-arms. Abyssal gains additional offensive powers, while aberrant gains additional defensive powers. This is why I had both of them sitting in the same place on my "top 3 bloodlines" pick as they are different flavors of the Bloodreacher.