Hard to say. I would probably say radiology (esp neuroradiology) or maybe opthalmology (though I really don't know that much about what they do to be honest).
Making a best/worst list is so subjective, it really is different for every person.
I think it makes the most sense to group specialties into medical, surgical, and other.
Medical specialties: Int Medicine and it's many subspecialties, Pediatrics and subspecialties, Family Med, Neurology. Tend to manage more chronic conditions, lots of mental masturbation over differential diagnoses and lab values etc, more emphasis on treating conditions with medicines than procedures in general.
Surgical specialties: Gen surg and subspecialties, ortho, ENT, urology, ophtho, neurosurg. Tend to manage more acute and short-term conditions. Too busy operating to spend inordinate time thinking about diagnoses, etc. Emphasis is on surgical management of problems in general.
Other specialties: Radiology, anesthesia, pathology, PM+R, Rad Onc, Psych. These are a varied bunch but don't really fit into the other 2 categories.
The only way you're going to know what's best for you is to do your M3 rotations and see what the various fields are like. Usually people can figure out pretty quick if they are more of a medical type or surgical type. those who are neither tend to do rads/anesthesia/path/etc.