Thought I should leave some feedback on heme/onc's behalf:
1. Lifestyle wise, Allergy is definitely better. Don't know if that is such a priority for people in medicine. I believe oncologist consistently have one of the highest job satisfaction among all fields. As stated above, most allergist work 4 day week, mostly if not all outpatient. Oncologist on the other end, work 5-7 days/week (mostly outpatient), depending on your desire for income.
2. Income: I think Heme/Onc, despite chemo not being reimbursed as a procedure, definitely has the upper hand. I know Oncologists central US making in excessive of 7 figures, although in popular areas (NYC, Southern Cali) starting salaries can be even lower than hospitalists...
3. Job Prospect: I think both subspecialties okay.. in more competitive locales it may not be that easy (again, Boston/NYC/LA) but around the country there are plenty of jobs, and I have not heard people in either specialty not being able to find a job in any location.
4. Competitiveness: Depends, allergy has less spots but also less applicants. In my program there were 4 AI applicants within the past 6 yrs, and all matched (2 of them without any research, from university affiliated medicine program, AMGs). I think if you are a FMG odds for Heme/Onc may be better, as research experience will outweigh the AMG status. But as AMG dont' expect to match in Heme/Onc unless you have some publications or are from a top tier program. Also Heme/Onc has more positions so it may be easier to stay within a certain locale.
5. Future: I dont think any subspecialty can match heme/onc in this aspect. You will see hundred of trials over a monthly basis on various chemotherapeutic agents... cardiology and oncology are the most well funded specialties when it comes to research...
Hope this helps...