Question is in the title
Polymorph
School transmutation (polymorph); Level sorcerer/wizard 5
Casting Time 1 standard action
Components V, S, M (a piece of the creature whose form you choose)
Range touch
Target living creature touched
Duration 1 min/level (D)
Saving Throw Will negates (harmless); Spell Resistance yes (harmless)
This spell transforms a willing creature into an animal, humanoid or elemental of your choosing; the spell has no effect on unwilling creatures, nor can the creature being targeted by this spell influence the new form assumed (apart from conveying its wishes, if any, to you verbally).
If you use this spell to cause the target to take on the form of an animal or magical beast, the spell functions as beast shape II . If the form is that of an elemental, the spell functions as elemental body I . If the form is that of a humanoid, the spell functions as alter self . The subject may choose to resume its normal form as a full-round action; doing so ends the spell for that subject.
Beuler? Beuler?
Dire Tiger's never a bad idea.
OffenseSpeed 40 ft.
Melee 2 claws +18 (2d4+8 plus grab), bite +18 (2d6+8/19–20 plus grab)
Space 10 ft.; Reach 5 ft.
Special Attacks pounce, rake (2 claws +18, 2d4+8)
Melee -> Dire tiger. Your a caster and so wont have the feats to make a hard single hitter work. So go with the tiger. You will get a bunch of attacks but beware you will not have a decent Str. Polymorph works differently now. You will only get a +2 Str bump to YOUR stats.
Basically take a look at Treantmonks druid guide. It gives good reasoning for choices on beast shape II and elemental shape I.
It's to cast on someone else. ;-)