If you have lower ceilings, and a short wall - I would go with the 6 inch.
But if you have really high ceilings, and a big wall space - the 9 would probably be okay, too. I suppose it depends on what type of look you're going for.
Another thing to consider...is your LO's name really long? If so, the smaller letters might look a little better.
...depends on the size and style of the room, number of letters, how they are being hung, etc. Try cutting out those sizes on paper and see which you like better.
Warning
No formatter is installed for the format bbhtml
I did DD's in letters I found at Walmart last year. THey no longer carry those and im having a horrible time finding letters to match for DS. Hers seem to be 7 1/2 inches and all I can find on hobbylobby.com are 5 1/2 and 9 1/2! I have no clue what to go with.
(Lurking a little early here...) I think it depends on the length of LO's name. I really don't like nursery letters where you can't even tell what they say until you're up close. Especially when people paint them or decorate them really busily or loudly. I feel like I have to squint to decipher some of them! I personally would just print a couple out on computer paper and hang them on your wall. I ordered mine online in 14" (and that's measured by the size of the smallest letter lol). Linus is a small name and I think they're adorable over the changing table.
Re: Nursery Letter Size?
If you have lower ceilings, and a short wall - I would go with the 6 inch.
But if you have really high ceilings, and a big wall space - the 9 would probably be okay, too. I suppose it depends on what type of look you're going for.
Another thing to consider...is your LO's name really long? If so, the smaller letters might look a little better.
Just a thought!