anyone have any suggestions on the best kosher resturant for an engagement proposition?
Mazel Tov! Although I've never been to The Box Tree, I hear that it's very elegant, and that the food & service are wonderful. It's also known to be extremely expensive. Much higher than any of the other upscale kosher restaurants. You might want to check it out.
(I also heard that in July, The Box Tree is planning to open another restaurant called The Branch, at the same location, where the prices will be more comparable to those of the upscale kosher restaurants.)
I agree that the Box Tree could be a good choice. Levana, while not holding the same cachet as it once did, could also be good place. If you're willing to pay a bit extra for it, see if they'll let you use their private room. My experience with them has been pretty good for making 'special arrangements' (i.e. my own marriage proposal) and they often can have some pretty good suggestions of their own. Check out their web site, and I know that they read their email (firstname.lastname@example.org) too.
B'shaah Tova U'mitzlachas!