When you look at sisters standing together (especially when they think no one is looking), do they look like they really care for one another or just want to "get through the party". This might give you some indication as to how close the sisterhood might be.
How do they make YOU feel? Like you would really fit in or they just want to make quota?
One of the long-standing difficulties with Recruitment (it's really rush most of the time, lol) is to be able to spend time getting to know strangers who you are about to pledge a lifetime committment to. Beautiful houses, super collegiate participation around campus and other things may be great, but the most important thing is sisterhood because without a strong sisterhood, the chapter won't last. Sometimes, the smallest chapters may have the closest and strongest sisterhood.
Good luck to you -- and go with your heart!