I'd go for walls then floors for the sake of keeping the floor clean also, and moreso the floor grout which is usually darker than the normally white wall grout, obviously, which is a pain in the back side to sort out if you get splashes on the floor. Never really bothered too much with the leaving the bottom row of wall tiles out though to be honest. Always siliconed those bits where applicable anyway so tend to just keep them a few mm appart no matter which way around it has been tiled so never really made too much sense to mix another bit of grout for the bottom tiles, or even worse, save the wall grouting until last.
I used to use dust sheets and white wall grout can be squished through them if you don't clock it and stand on it. So always used to aim to
tile and grout the walls before setting out the floor.
Obviously that's when you're not using same tiles throughout and need them to all marry up in which case I've even started to
tile the walls and the floors kind of at the same time even to make sure they're marrying up well on as many walls as possible (normally end up with one of the walls not running so neatly against the floor so tended to have that the door wall so you couldn't see it when walking in).
Did a stupid job ones using 100x100mm uneven floor tiles in a tiny showeroom / wetroom (had jets in the wall and 'downlighters' in the walls instead of the ceiling). But then on the walls they were like 400 x 200mm matt smooth porcelain. The room wasn't square at all, not a single wall was square with another and to make matters worse there was a false wall in the middle to make the shower area closed off which was at an angle so a sink could fit in the corner of it the other side next to the loo. A really right room for what was in it really. Took about 2 days to set out and we ended up cutting some
tile to make the lines marry up but you could never stand in the position to see it as the room was so small, you could only really look at it from the doorway as you walked in, or from the shower. So we made those area's perfect and then managed to cut the rest to fit.
And as it was one of the first tiling jobs I did I was the dedicated cutter! Got soaked for a whole week. Day after day. I didn't even want to stop for food as my clothes were soaked and I'd rather just get on with it.
An architect it was for. Very nice house in the end but everything was a maul in it. All the blokes that worked on it had similar sort of random issues that had to be sorted out by them.