He gave us a small intro on how PF was all better than 3.5, but to me it just seems like someone without any real knowledge on how to design games properly went through the core books and changed things randomly. I may have to reconsider making a druid, as they seem to get nerfed hard.
You understand D&D better than your DM. I just want you to keep that in mind for the rest of this thread. Chances are, builds that have a high damage output will be banned. So will builds with a high AC. Enemies will likely rely on high AC and being giant sacks of hit points for their defense. You will want to invest in battlefield control and debuffs at low levels for your offense, so that moderate damage output will destroy your opponents. Your defense will be battlefield control again, as well as buffs. When you get access to them, miss chances are good. At higher levels, save-or-dies and no-save-just-suck abilities become more viable, and touch ACs fall further and further behind (so that attacks that rely on them become more and more powerful). Your defenses will become more tactical than statistical; use spells to reshape the battlefield or fly, so that enemies can't reach you. It's likely that several opponents will lack flight capability altogether, but not certain. Do things like give yourself Superior Invisibility, or the Darkstalker feat, and so on to prevent your opponents from knowing where you are. If you can get somebody undead in your party (Necropolitan is a good way to go), Lifesense (see Libris Mortis) is a fantastic feat to take, but it's likely intelligent undead weak enough to be PCs will be banned, and the DM will argue that a rotting corpse isn't socially acceptable no matter what you do, making no allowance for things like Bluff and Disguise checks or
gentle repose. See if you can get access to summoning Earth elementals, and make use of Earth Glide to harass your foes. Summon Undead for allips or shadows or something works just as well.
I would recommend having at least 1 Tome of Battle character in your party, but be warned that there's a decent chance it'll be banned. Barring that, druids are excellent at low levels, and while they lose some of their luster at high levels compared to wizards, they're still solid choices. Wizards are going to be extremely powerful in the late game (Celerity is an especially tasty gem), but their fragility at low levels can be problematic before they get enough spells that they never run out, and it seems likely that your DM will steal your spellbooks at some point. Meanwhile, the druid can just grab any tuft of fur (note that your animal companion is likely to be covered in them) or plant (note that the ground is likely to be covered in them) and call it good.
In short, unless you're starting at level 15+, I'd recommend druids for every possible party member.
EDIT: Another reason is that, barring shenanigans, Wizards have a hard time getting access to large amounts of healing without magic items. This isn't so important in battle, but it compounds with their fragility to greatly shorten the number of combats they can fight. At any rate, stick with casters; if magic items are rare, noncasters are screwed; a Fighter of any non-epic level is screwed against a Balor, but can you imagine how fast that fight will be over if the fighter has only a masterwork sword and masterwork suit of full plate? Spellcasters get to keep their toys.