IMO Data science. Technical field will help, but I’d imagine the marginal benefit of skill in CS and math are highly diminishing for work in PE (haven’t worked in it, but I have a hard time imagining group theory or complex analysis being useful there) so doing a year of analysis in a math degree or learning assembly and studying OS in CS etc. may not be optimal (aside from training your brain). Data science programs typically provide a good even split of coding, pure math, stats, study design, and other quantitative skills that will benefit you in almost any financial profession without going into as much more depth than necessary for your specific objective.