For me it is Hegel and Nietzsche, and their successors. For me it is the major split in the Western tradition today, and whoever can reconcile them will 'win' philosophy for this generation.
To put it in a way horribly simplified (obviously the trees branch out, and I am interested in the other branches too -- most impressively absent is the French lineage going through Sartre, Lacan, Debord, Baudrillard) there are two grand lineages operating at the moment, on the order of :
Hegel --> Young Hegelians --> Marx --> Zizek. I will call this the Red tradition. It influences the socialist Left, the totalising left, the grand systemic left. It is interested only at the highest levels, societies, histories, collectivities. It has no time for the individual.
Then there is Nietzsche --> Heidegger --> Foucault/Deleuze. I call this the Black (anarchist) tradition, because it is concerned with the individual and the nature of their entrapment within power flows. Lots of other anarchists I won't mention here are also Nietzsche-inspired.
The Hegelian is about negation-unification, teleology, and trying to see it all as one system. The Nietzschean is about affirmation-splintering, anti-teleological, and about trying to hold on for the ride as our reality and social body increasingly fractures and fragments. I like both a lot.
I read Nietzsche when I was about 20-22, and his views influenced me a lot. Recently I have been going into Hegel and Marx and their successors, and I am finding not so much a 'disagreement' but a tension, a dialectical kinda thing. It is fascinating and I hope we will have some kind of movement on this front in my lifetime.
Honourable mention: Wittgenstein (for killing the foundations of analytical philosophy stone dead, TWICE), Whitehead (for inventing Hegelianism in reverse before he died as a fuggg u to Russell), Spinoza