doubling the toughness improves survivability by a surprisingly wide margin, and again, my favorite thing is how clean of a signal it is. It's not just an increase in toughness, it's a signpost.
For the record, Accorder Paladin feels like it's almost there for me. The effect is really good in aggressive deck, as well as the power, but dying to, say, Darkblast (read: all removal) is annoying. I can imagine the Crop-Captain plays well, and I do agree it's a nice signpost.
Temmet, Vizier of Naktamun - Jumps your biggest creature every turn and plays well with equipment and auras. The embalm gives you value in the late game and gives you a form of reach.
Winding Constrictor - Heavily signals a counter theme and can let cards get way out of control really fast. Dom Harvey wrote more about the archetype here.
Veteran Motorist - The scry 2 is really valued in aggressive decks. The body is definitely fragile but still super aggressive. It signals a vehicle theme which can signal greater artifact shenanigans.