The top two of that selection is for sure the Lincoln MKZ and the Cadillac ATS. Just depends on shape preferences, if you like more round and modern then the MKZ will do and your looking for more square and bold the ATS will be for you. Hard to say as I chose the MKZ but sometimes it's just hard.
The Toyota Avalon is not appealing at all. some weird shapes and designs they are using. To me it just doesn't scream luxury. I know it must have a nice interior and all but the exterior seems no different than a camry or corolla.
The ATS is nice If I had to pick something else besides the MKZ it would be the cadillac.
Best looking are definitely the Cadillac and the MKZ. I think I might like the look of the Cadillac more. The others just aren't that striking. The worst is the Toyota. Maybe if we saw some of them in different colors it could change my opinion slightly.