There are many intangible rewards like seeing the families of patients grow, many tangible ones like your office being full of presents during the holidays, you get to make your own hours, and the job is very relaxed and mostly stress free. It is boring though, since you will rarely see anything beyond otitis, acne, and malingerers.
On the other hand, internal medicine is very complex and you should not go for it unless you relish a challenge. Also, hospital practice is markedly different - your patients will be invariably ill and you'll have to deal with death on a daily basis. And then there's teaching responsibilities.
If you would like elements of both and don't mind dealing with radiologists, you would probably do very well in oncology.