Its great to see my favorite class getting some love! Walters guide is great, but it was getting a little outdated, with some of the new tricks Magi can get such as Arcane Deed. You may have already seen it, but I use this guide for reference when it comes to the various polymorph spells.
I don't think elemental body lets you keep your gear (though I would like to be proved wrong), so unless you want something specific I dont generally think its worth it. Monstrous Physique is my favourite, particularly for a strength Magus, the stat ups are great, and forms like 4 armed gargoyle can seriously boost your DPR. (though In that form, I prefer to use the spare hands to THF with my main weapon, hold a metamagic rod and still spell combat rather than get a barrel of individually meh attacks usually). You can get pounce, but few Monstrous Humanoids seem to have it, and the only one I can find might get banned by some DMs due to setting constraints (Tikbalang). Beast Shape= no spellcasting which utterly sucks, so I cant see it ever being a good combat spell, but it could see some good utility use. I have used small and tiny forms for stealth/infiltration a few times to good effect, for those levels where see invisibility is a problem but true seeing is not. I have never used the undead one.... might see if i can find anything.