I always think Three makes it look like three people sleep across.

If you want simple and serene, scroll down about half way to see pps7's master bedroom in the thread linked below: white bed linens, 2 sleeping pillows, 1 decor pillow and a light taupe covered duvet.

Here is a link that might be useful: Guest room queen vs. king bed?

I would agree that two are sufficient. It always seems strange to me when hotels make up king beds with three (regular) sleeping pillows instead of two king pillows.

It's purely personal preference, but I like the look of three Euros on a king bed and two king pillows.

Fun2BHere summed up what I was thinking.

I did a row of 3 euros across our king bed, then 2 king pillows in front of those, which sufficiently filled the space between each side of the bed. I initially tried only two euros but no matter how I tried to arrange them they just didn't fill the space to suit me.

That is too funny. I've never thought of it looking like 3 people sleep in the bed.

When I was helping DD set up her guest room, I made 2 euro shams for her bed. I now regret it. I think 3 would look much better.

Only as many as people who will sleep in the bed.....three looks like a party.

On a king bed.. three euros. Two just looks skimpy to me. The euros are more of a "plush headboard" kind of action and should fill the back of the bed.
A couple king pillows or two pairs of regular pillows for the regular sleeping action.

My hubby and I go for comfort over looks- three plush headboard pillows, two regular pillows for sleeping each, and I have a king sized pillow on my side to prop my knees when I need it.

Thanks for the props javachiks, I have 3 euro pillows but end using 2 most of the time. Honestly, I'm not much for making beds. I just pull up the duvet cover. I would get three initially and play with it. I do think 2 looks fine.