I also use the Escape key. It’s fine for me, I mean, that key is dedicated to dismiss stuff 
Using the same key combo to dismiss the LB window would be conflicting:
Many people are using ⌘Space as the LB hotkey. And, once the LB window is on the screen, Space as well as ⌘Space gain a different, special meaning:
Space: Depends on the item in focus, for example…
- Internet search query, iTunes, App Store: Opens a text field, where you can type in the search string
- Mail, Twitter: lets you type in the message text for a new mail/tweet
- Safari: shows you the bookmarks
- Keyboard Maestro: lists all KM macros
- Terminal: lets you type in a command
- Most other apps: lists recent documents
⌘Space: Shows you a list with the recent apps launched via LB