Fastest
1. Portugal: 5 years residency (standard). Visa options available (digital nomad, investment). Processing fast if eligible.
2. Spain: 5 years residency. Easier if married to Spanish citizen (3 years).
3. Greece: 7 years residency. Can reduce to 5 if married or parent of Greek citizen.
Hardest
Japan: 10 years residency minimum. Tests Japanese language (N2 level). Must renounce prior citizenship. Very restrictive.
Switzerland: 10-12 years residency. Varies by canton. Difficult language requirement. Tests cultural knowledge extensively.