Definitely read through this thread:
You may want to check out this thread
I've been somewhat disappointed with most tapas restaurants in Chicago, compared to what I've had in Spain and in San Francisco. By far, Cafe Iberico is the best, in my opinion. I've never been disappointed with the food; just the long wait. The wait can easily be an hour and a half on a Saturday night (but it can also be a lot shorter than what the hostess tells you it will be).
I was also very impressed with Azucar the one time that I had it.
Avec is strictly speaking not a tapas restaurant. The food is more contemporary, but it is served "tapas style" - meaning small plates - and the food is certainly inspired by Spanish and southern French cuisines.
Unfortunately, Spanish food is not one of the strengths of the local culinary scene. Are you open to other cuisines (especially regional Mexican or Thai)?