Best Summon

Ok my conjurer can now cast Summon Monster 5. I am torn between about 4 critters being the cream of the crop - the azata, a dire lion, a babau demon and the dinosaur (ankylosaurus or somethin - the one with the club tail). I also have the spell animal growth. Any thoughts as to the best of the bunch?

I like the babau demon the most for dispel magic at will. Summoning one of those means a good chance at locking down an enemy caster while you continue to function as a spellcaster yourself.

Also the ankylosaurus has a tail which does 3d6+x damage. if it sizes via animal growth, what does the new damage become? I looked on the natural attack table but it listed a lesser damage for a huge creature. This creature is intriguing to me because of the stun attack.

1d4+1 Lantern Archons.

Lets say you get 3. That's 3 ranged touch attacks that ignore DR on the first round (or they can just aid themselves). On the next round you get 6 of the same touch attacks. By the time you are done you've gotten a possible 54d6 damage out of them. They have some nice immunities, fly speed, DR and are generally useful all around.

Dire Lion is pretty great for dealing damage as far as summons go because you get smite evil (+8 damage) on every attack on a pounce against the first thing it decides to shred.