It depends on how long you expect the campaign to last. If you're really hoping for 9th level spells and you don't know how long it will last, you'd better just take your first 17 levels as druid. If you think it will go to 20, you have more flexibility. If you think it will go into epic, then what's the hurry?
Here are some ideas:
Nature's Warrior 4: Better than 3 because you get an extra point of BaB, an extra spellcasting level, and extra bonuses (+4 natural armor instead of +3, for example).
Warshaper 2, 3 or 5: Yes, Warshaper 5 hurts your spellcasting a lot, but the ability to change once per round effectively gives you unlimited wild shape uses. Even better, that ability works with the entire polymorph tree. Think about it - Alter Self that lets you change at will, or Polymorph Any Object that lets you change into absolutely ANYTHING as many times as you want. Also, you might argue that it lets you Shapechange twice per round -- once as a free action, and once as a standard action.
Master of Many Forms 1: Speaking in wild shape is very useful. Speaking any language you want just by turning into something that speaks that language is even better. And depending on your DM's interpretation of the rules, Nature's Warrior might advance the Wild Shape abilities of this class, making MoMF1/NW5 almost as good as MoMF6/NW5.
Master of Many Forms 3: Changing as a move action is nice, especially when combined with Warshaper 5. WS5/MoMF3 is like mini-shapechange. And don't forget that with Wilding Clasps, you can wear magic items in Wild Shape. You can't do that with Shapechange.
Master of Many Forms 5: Nice if your DM allows it to stack with Nature's Warrior. You invest 10 levels into wild shape with only 2 spellcasting levels to show for it, but in return, you have 5 levels of full BaB and MUCH better Wild Shape than a 20th level Druid. In some ways, your Wild Shape is better than Shapechange (Wilding Clasps, NW bonuses, speech, no HD limit), Of course, you'll have to wait until level 25 to get your 9th level spells.