Crete is the largest Greek island. A 7-day trip from one base can't cover the whole island. Here's the honest map.
Chania — for atmosphere and west-coast beaches
Chania is the prettiest Cretan city — Venetian harbor, narrow lanes, dense restaurants. Stay in the Venetian Harbor for the photo or Splanzia for value. Best for: first-time Crete visits, romantic stays, west-coast beach access (Elafonisi, Falassarna).
Heraklion — for Knossos and central Crete
Heraklion has Knossos 20 min away and the Archaeological Museum. Less atmospheric than Chania but central. Best for: Knossos-focused stays, ferry connections, central-Crete day-trips.
Rethymno — for the middle
Halfway between Chania and Heraklion. Smaller than both, with a Venetian harbor and a real old town. Best for: travelers who want one base for east-and-west day-trips.
South coast (Plakias, Loutro, Agia Galini)
The south coast has Crete's most-dramatic landscapes — Samaria Gorge, Preveli beach, calmer than the north. Best for: hiking-focused trips, anyone wanting non-tourist Crete.
Strategy
For 7 days: pick Chania for west-focus or Heraklion for Knossos-focus. Don't try to do both in 7 days. For 10+ days: 4 Chania + 3 Rethymno + 3 Heraklion is a solid loop.
Compare: Heraklion overview. For broader Greek island context see Greek islands which to pick.