After the discovery of the Higgs boson a new era of precise measurements has been started at LHC. The upcoming update of the European Strategy for Particle Physics will chart the future in the field at the high-energy frontier for the coming decades. The physics potentials and the key differences between the proposed linear or circular collider were evaluated at the various reachable collision energy. Hadron or lepton machines are confronted on their sensitivity to precisely measure the Higgs boson couplings and the possibility to make direct or indirect discoveries. Demanding technologies, bright solutions and vigorous R&D will be needed to launch such challenging projects and pave the future for novel accelerator concepts. The international scenario will be sketched with a personal view to stimulate discussions and suggestions.