I change my mind all the time and I haven't even started med school yet. They are ranked according to my current preferences:
1.) Neurology- probably my number #1 choice right now because I've always found the brain and its diseases fascinating
2.) Forensic Pathology- no hospital pathology for me. I want the weird cases that no one wants to see or hear about. I want to work alongside law enforcement and be able to testify in court (although most Forensic pathologists tell me that the testifying thing begins to wear thin). Pathology provides sort of an intellectual challenge in that you are given a bunch of clues and have to determine cause, manner, and mode of death.
3.) Emergency Medicine or maybe Trauma Surgery- I think I would like the high paced environment and having to think/act quickly
4.) Oncology or maybe Immunologist- or something similar where you would be able to work with the immune system. The immune system is probably the second coolest system in the body behind the nervous system. Reading an immunology textbook is like watching an action or war movie. There's all sorts of killing going on.
5.) Radiology- I doubt I would enjoy this, but whenever I take those tests, this comes up as my #1 choice, so who knows.