As a girl, I have to say that I'd much rather have my BF propose, oh pretty much anywhere, other than a restuarant. And for me at least, it's not the crowd of people. It's the originality, or lack thereof. We want to think that you actually worked for us. You know? Something really creative or unusual.
Think about these things:
When you met: Where? When? Anything unusual about it?
Your first date: Where? What happened?
And if neither of those options were particularly eventful, how about any quirky, fun, special, crazy moment in your 4 years together that you often talk or laugh about. Try to replicate these special moments somewhat.
And if all else fails........ here's one I thought would be kind of cute:
You get her a star from the international star registry. Instead of her last name, have the certificate say her first name and YOUR last name. Take her to the planitarium, or if your city doesn't have one, someplace at night where you can see plenty of stars (weather reports will be handy in deciding a day). Give her the star registry and while she's looking at it, take a knee. When she sees your last name, she'll be confused and look up. When she does, have the first sight she sees be the ring. Then say something mushy like: "I wanted to name a star after you, but I wanted to be sure the name of that star would be the same forever. So, the star is called "Jane Doe", because if you'll do me the honor, that will be your name forever."