Goosefoot or El Ideas
Two outstanding venues; been to both 3-4 times each and love them, but they are very different. While both are BYOB, Goosefoot is a more traditional restaurant - think of it as somewhat laid back fine dining. Chris Nugent's food is IMHO the best tasting food in Chicago. El Ideas is more of a dinner party atmosphere than a fine dining ambiance. You can hang out in the kitchen between courses and the chefs present each course. The food is very modern and experimental, but generally excellent. The location of El Ideas is a bit out-of-the-way which is a turn off to some. Both are fantastic and it really comes down to if you want a more traditional type setting or a dinner party like setting.
I've not been to Goosefoot but we were at El Ideas last week. Had a great meal and a great time. Food was excellent -- unusual flavor combinations but nothing too outre. Not sure that I'd describe it as "romantic," if that matters, but certainly a comfortable, welcoming atmosphere -- conversation friendly. Would definitely recommend it (and the reservation is easier than GF, which was where we'd initially hoped to go).