Yes pay, respect, and lifestyle.
Unfortunately, I don't know enough to comment on specific salaries for the other fields...but I believe Heme/Onc generally makes more than Allergy, Endo, and Rheum (chemo reimbursment, etc).
Respect/prestige is a non-factor for me and totally subjective as well as silly. Now if we're talking "sexy," then none of these fields compare to Cards or GI
It's kinda like asking if the 2nd to last kid picked for dodegball is more cool than the very last kid picked (maybe not the best analogy).
If you insist on some sort of ranking though, Heme/Onc is considered more competitive than the other 3... I can see jdh71 rolling his eyes now.
Also, do you have any advice for interns to maximize our chances for the Heme Onc match. Any advice to help from your experience and talking to successful applicants that you talked to would be appreciated. Thank you very much.
Research, research, research. You don't even have to be published by the time you interview. Just make sure you get into a lab (basic science seems to be the best for Heme/Onc) or jump/start on a project w/ a well-known faculty member in the field you're interested in. When I was at MSKCC and other top notch programs, everyone seemed to be an MD/PhD or had amazing research backgrounds. What seemed to blow it for me last time was a lack of significant research. You can say "academics" till you're blue in the face, but if you don't have any significant research to back it up it doesn't matter.
If I had to do it all over again, I also would have gone to ASCO/ASH each year to get a feel for who the big names are in the field. It also doesn't hurt to network by presenting posters, etc. I HATE HATE HATE playing the game, but that's what you have to do for the more competetive fields.
Lastly, have your game face on ALL THE TIME during residency. There are a lot of people who will tell you they only care about doing well while on their elective/rotation of interest...that's BS. You should bust your butt regardless of who's watching...and be consistent. Your colleagues and attendings notice = excellent LORs. Might also make the difference between someone being willing to go the extra step and make a call on your behalf. I can't stand people who think learning about the other aspects of Medicine is beneath them.
Time to get off my soapbox. I'm interested to see what others think. Good luck!