What to Polymorph other into?

[Shard O'Glase]

You should definitely be sure to look at the current official Polymorph Other spell. It is in Tome & Blood, Dragon #280, and here, at Eric's old Black Pages (the only place online, ASFAIK).

I think Grig is one of the best for a mage, though one of the smallest dragons could be cool as well (as they're able to cast spells, as well).

Of course if you Polymorph into a troll, you could multiclass as a fighter.

Pixie is better cause then you aren't some 1/2 ugly bug thing.

 

[Henrix]

Pixie is better cause then you aren't some 1/2 ugly bug thing.

A but a pixie is small, while a grig's tiny. You don't want to miss out on that extra +1 AC/Attack bonus!

We're talking min/maxing here, not some sort of personal feelings!
Besides, I think grigs are cute.

But a pixie flies faster and with better maneouvreability.

 

[Arcanus]

I would go with the quickling if the Dm allows it. The stats are in the Creature collection.