The scientist — research-driven (primary or meta-analyses), with publications in peer-reviewed journals e.g. Gottman academic papers, Eli Finkel, Joanne Davila. They invariably venture into pop texts which build (and at times hyperbolize) on results from their scientific studies.
The specialist — sample-driven, with training in a relevant field layered with insights from professional experience working with different couples, e.g. Esther Perel, Stan Tatkin. Be mindful of selection bias in the context of general conclusions, since their samples are skewed (only a certain type of couple can afford to go to a world-renowned psychiatrist).
The sage — wisdom-driven, often thinking about relationships from first principles or from the vantage or a personally held life philosophy, e.g. Alain de Botton, Seneca. What they say will usually strike a chord and may sometimes be contrarian.
The spiritualist — energy-driven, the proponents of masculine and feminine dichotomies and channelling your inner god/goddess. Rarely substantiated by anything concrete yet may still resonate with certain personalities.
The synthesizer — community-driven, they do the work of consuming the (often dry) material from academic journals, philosophical texts, etc. and connecting the dots, e.g. the author of this blog. They then popularize what they personally find interesting/compelling to a wider/different audience.
The sassy stylist - significance-driven, they extrapolate from their own experience and the experience of a very limited group of other people (friends, family) into purportedly general-purpose advice, e.g. Reddit, Quora, your barber, your work bestie Rebecca.