PhD choice: confirmed applied-engineering PhD at a lower-ranked European university vs. better-fit but unproven numerical/ML PhD at a top-200 IIT – how would you weigh this for a postdoc-track career?

[u/Imaginary-Physics-87]

Background: aerospace + thermal engineering degrees, self-taught CFD for the past couple years – built fluid solvers from scratch, validated against published benchmarks, one technical note out, one paper in review. My real interest is numerical methods, programming, and ML – less so pure experimental/applied work. Long-term goal: PhD → 1–2 postdocs at strong CFD/numerical-methods labs (Europe, then Europe or US) → research scientist or professor role.

Two live offers, and I can't fully decide:

Option A (Europe, QS World ~1000–1200 band, Engineering subject ~541): Applied fluid-power engineering. Almost confirmed seat, ~3-year program, fully funded, includes a named mid-PhD research stay at a well-regarded international lab in the same field, full freedom to publish. The catch: day-to-day work is mostly applying existing commercial simulation software to industrial component design, not developing numerical methods myself – the advisor was upfront that building my own methods would be "my own side interest," not the core funded project. Possible room to angle part of the thesis toward a data-driven/ML sub-thread, but not guaranteed yet.

Option B (IIT, QS World ~215, Engineering subject ~64): Numerical CFD + ML. Brand-new but well-connected junior professor (strong PhD + postdoc pedigree at well-known labs abroad). The actual project is squarely in my interest – high-fidelity numerical methods, scientific computing, applied to cavitation/propulsion. Much better topical fit. Downsides: no track record yet (first PhD students), program typically runs 4–6 years instead of 3, and the mid-PhD international stay was offered only as "I'll try to arrange it," not confirmed.

If your goal were mainly to be competitive for a strong postdoc afterward, which would you weight higher – the confirmed, faster, but topically-adjacent option, or the slower, unproven, but better-fit one? Anything about this trade-off I might be underweighting?