The vanity is usually 21" deep and the current toilets are close to 30" deep. 30 for toilet + 32 for door is 62" and then you have a few inches to play with but it's cutting it closer than having a bit of wall next to the fixture before the doorswing.

If the door is open you see the vanity from one approach and the door from another rather than the toilet first thing from one of the approaches.

If you open the door when someone is using the toilet, they will be shielded a bit by the side of the vanity. If you open the door and the toilet is first in line, not only would you get a full view, you would knock them pretty hard on the knees.

If the side of the toilet gets wet or steamy from the shower or bathtub on a repeated basis, it's no big deal. A vanity next to the tub that may have some damage to it's finish over time. My friends in Manhattan have a vanity a few inches from the side of the tub and even with the shower curtain, there is almost no finish left on the side of the vanity (I'm sure it's a cheap builder's vanity though)

It's nice to be able to put your folded towel on the closed toilet seat? That probably seems minor but I tend to put it there rather than on the floor.

I thought I figured it out: water! Duh!

But those other points are perfectly valid as well. :)

We are planning on some sort of pony wall with fixed glass above it on the shower by the vanity side that I would butt the vanity against which should protect it from the shower. No tub on this one; we're trying to do a curbless or low-curbed walk-in shower and make it moderately accessible (we won't manage ADA but it'll be a guest bath for aging relatives).

Planning on a pocket door which helps with some of the door issues but opens up a few more.

Thanks, Pal. I will have to investigate sightlines and elbow room!

We have almost the exact dimensions in the bathroom we're adding, and I admit that for aesthetic reasons alone, we'll be using the typical layout of toilet between vanity and tub. ;)

But I think even people who don't care as much about the aesthetics of seeing a toilet through an open bathroom door, prefer the toilet to feel a little more private. So, tucked in between a shower wall and a vanity is better than out in the open at the entrance to the room. (Even though that's a little illogical, as long as the door is closed!)

And if you're worried about accessibility, then putting the vanity closest to the door makes much more sense. Since the toilet will stick out more than the vanity, putting it in the doorway creates more of an obstacle for someone to maneuver past to enter the room. With the toilet tucked in between the vanity and the shower, you gain breathing room in front of the vanity (in what is, in a small bath, the main part of the space).

It's also been my experience assisting a person in a wheelchair that the typical path is toilet and then lift into the shower chair, so having those closer together really helps. (Even if you're using a bedpan under the shower chair, you will very much appreciate having the toilet as close as possible for emptying it.) I can also imagine someone with a cane or balance issues using the (lidded) toilet as a post-shower perch for drying off.