Your own satisfaction is a function of your interests and your personality. I know born surgeons, and surgeons that despise every hour of their working day. There are internists who reach orgasm at the most seemingly minute piece of clinical data, and internists who are bored out their skulls.
In terms of "making a difference", that's also a subjective thing. A public health doctor can theoretically save millions of lives. A family doctor that's engaged with his or her patients can make a massive difference, particularly if they work with the poor.
Gratitude from patients is the only one of your questions with a somewhat predictable answer, though the answers might change between jurisdictions. Heart surgeons, for example, will almost always be put on a pedestal by their patients. Oncologists walk on water, depending on their practice patters. Family doctors are always valued, especially in rural areas. Psychiatry, however, is not a field to go into if you're looking for patient gratitude. Maybe they do okay in private practice, but psychiatrists dealing with bipolar or psychotic illnesses will never get chocolates at Christmas.