I would steer away from places where the food and its presentation require all of your focus. While Alinea and the like are certainly great dining experiences, those type of scripted meals are very intense and demand your complete attention. Under the circumstances, you may want to spend more time concentrating on your dining companion, rather than the details of the meal itself. I would go with something more relaxed and accommodating with a cozy room and a nice view. I would throw North Pond back into the mix. It has an intimate and welcoming vibe in a one-of-a kind location. It is in an actual historical Prairie School Arts and Crafts style building on a pond in the heart of Lincoln Park overlooking the city skyline. The dishes themselves are upscale modern interpretations of Midwestern comfort food. Truthfully, I have not eaten at most of the other places mentioned, some are just not "my thing", however I have always found North Pond to be romantic in an elegant and charming way, maybe that is a little clichéd, but sometimes clichés do work.
Of the other places that were mentioned, that I have not dined at, El Ideas appeals to me the most. While it may not be trendy, it is certainly unique. The menu is fixed and changes every night as new dishes are added and others are retired. There is only one menu, and the entire room is served each course at the same time. Before each course is served, the chef who developed the dish announces it and explains his philosophy and intentions behind the design. Sharing a communal experience with a group of fellow culinary adventurers, has the potential for an interesting evening, if you are open to meeting new people. Again, it might not be the perfect environment for a proposal of marriage, however, celebrating the moment with a group of strangers has the potential for a memorable experience.