Best forms for Shapechange?

[RumpinRufus]

I'm about to have Shapechange as a domain spell, and I'm looking for suggestions on how to make the most of it. Being a dragon will be awesome, but I'm wondering what other forms people find useful. The spell lets me change form once per round as a free action, so there's tons of flexibility.

The available forms (and the possible abilities I could gain from them) are:

Spoiler:

Magical Beast (Tiny to Large): burrow 60 feet, climb 90 feet, fly 120 feet (good maneuverability), swim 120 feet, blindsense 60 feet, darkvision 90 feet, low-light vision, scent, tremorsense 60 feet, breath weapon, constrict, ferocity, grab, jet, poison, pounce, rake, rend, roar, spikes, trample, trip, and web.

Air elemental (Small to Huge): fly 120 feet (perfect), darkvision 60 feet, whirlwind, earth glide, burn, vortex, energy immunity.

Dragon (Medium to Huge): fly 120 feet (poor), blindsense 60 feet, darkvision 120 feet, a breath weapon, DR 10/magic, frightful presence, energy immunity, bite (2d8), two claws (2d6), two wing attacks (1d8), and one tail slap attack (2d6).

Giant (Large to Huge): swim 60 feet, darkvision 60 feet, rend (2d8 damage), regeneration 5, rock catching, and rock throwing (range 120 feet, 2d10 damage).

Plant (Small to Huge): darkvision 60 feet, low-light vision, constrict, grab, poison, DR, regeneration 5, trample.

Obviously there's hundreds of choices and the best one will depend on the circumstance, but I want to have a few prepared beforehand so I don't have to spend too much time looking things up in-game. Any suggestions on some good forms to take?

[Bloodwort]

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Personally, since "shapechange" is a 9th level spell, I would also suggest that the other polymorph spells like "monstrous physique" and the undead one, and the vermin shapes would also be permissible.

I vote that Paizo should errata this into "shapechange" abilities.

[Peasant]

It's hard to see why you wouldn't normally go with anything except an assortment of dragons, given that shapechange doesn't give you access to any of the more bizarre abilities that make many monsters interesting and unique. That said, vortex (air elemental) and trample (dire elephant) are both excellent crowd menacing and board control abilities. If you've been summoning recently, turning into whatever you summoned, then turning into something inconspicuous (like a vole) just as they despawn might leave your opponent's guessing.