I would see what the faculty staffing situation is for both of those services before making a decision, but I’d lean toward surg onc. A lot of ICU’s have rotating weekly attending coverage, which could make it hard to get to know a single attending well enough to have them write you a strong LOR. It can also be hard to stand out in the ICU as a student. You’re pretty much judged solely on your presentations (the goalposts can change every week with the attending) and the subject matter is often difficult. Surg onc will probably give you more continuity with one or two attendings so you can get a good letter and you’ll get the opportunity to show your skill in the OR, at rounding, presenting, and working up consults/clinic patients.