Understand what a PhD is before asking such a question. It's a topic in depth for 3-4 years. As such, the "best" phd is one where
A) it's something you like
B) something you're prepared to lecture or research in if you don't become a quant. Face facts, this positivity stuff of "you can do anything" careers advisors bombard people with is horseshit and one of my quant bosses even used to say about some people we interviewed on with strong maths backgrounds "they'll never become a quant" if they don't have a classical quant background. Also, a PhD can lead to a narrower range of options than a degree in hr would. If markets are ok, it's not an issue. If markets flop you'll be scrambling around looking for alternatives that may not exist.
Also on B) this business of planning to go into Job 1, Job 2,... quant or Phd/Msc/MFE -> quant that I sometimes see on boards like this is fraught with risk. Risk the map to quant you're planning is out of date. Risk that map will change over those 3-5 years of research. And risk you spend so much time job hunting that you don't finish the phd. Anyone I know that did well in industry from phd had originally planned to lecture and stay in research and went into industry because lecturing isn't all it's cracked up to be, not as part of a plan to be a quant prior to phd, sorry.