These 2 fields can be compared under following headings... I was also in ur shoes last year. I could not convince myself to choose invasive cardiologist (with stressful lifestyle), and picked hemonc over non invasive card for my future...So my analysis is likely biased toward hemonc
Field choice; Its a personal thing. One have to do elective to see what he/she likes based on quality of life/reimbursement/future. All charm of cardiology is in Interventional cardiology (more money also upto 800k in south). Someone can put hemonc higher than non invasive cards (which basically is close to IM, especially if in future, medicare says all caths should be done by invasive cards so he can place stent at same time/no diagnostic cath. One can put non invasice higher as still lots of stuff echo/stress test/variety than hemonc (hemonc depressing, but only inpatient not out pt, hemonc in pt where resident rotate and hate hemonc is actually hospice service in most cases. To see real hemonc one should to dlinics as 90% hemonc is outpt. Hemonc have also variety with 100 different kind of cancer with 1000 different treatment with every pt responding in a different way....
Competetiveness: cardiology is more competetive in most programs than hemonc. Though residency program, usmle score matters more in cards and research experience matters more in hemonc. Links work in both
Lifestyle as a fellow. In most program, at least in my university, cardiology fellows work more than hemonc fellows.
Lifestyle as attendng: hemonc have more controlled hours with more out pt practice/less stressful cases than non invasive cards. Less chances of law suites. In Academic again hemonc enjoys better lifestyle than cards.
Reimbursement: A broad range in both fields especially in private practice. From my program fellows going to academics from both hemonc and non invasive cards starting salary was 200k to 250k. In private practice non invasice cardiology fellows got starting offers from 300 to 450k. In hemonc I can put exact sallaries region wise for fellows going from my program ; Florida 280k, Florida 375k, west vergenia 500k, vergenia 280k, Gerogia 420k, and one fellow went to far far place at 620k but neares airport was 4 hr drive from that place, and mcdonald was biggest resturent.
Pay cuts: Are affecting both fields but physicians always find different ways to make money...starting salaries are going higher in both fields
On the other hand a hospitalist have more controlled vacation time with 14 day on 14 day off which both these fields dont enjoys as both fields have continuity of care. In my program I saw a hospitalist who see 88 patient in hospital a day, likly make 500k and consult all consultants to manage his pts and have 2 NPs to do H&P and D/C summaries
Most important thing is one should like what one decide to do for whole life....