Italy and Greece are both Mediterranean summer classics that get marketed interchangeably. They aren't. The trip type each rewards is different, the mistakes you can make are different, and the right pick depends almost entirely on what you actually want.
Here's how to choose.
Pick Italy if
You want cities and history first, beaches second. You're traveling with someone who needs more variety than just sea-and-relax. You want walkable old towns where you can do dinners-out for a week without repeating cuisine. You have 2+ weeks and want range. The trip is built around food and art rather than swimming.
Italian summer cities are punishingly hot but they have indoor culture (museums, churches, restaurants with AC) that Greek islands don't. Rome and Florence in July are doable; Mykonos in July is sea-and-sun-and-not-much-else.
Pick Greece if
The trip is about the islands. You want a slower pace, a single island for a week. You're a couple on a romantic stay or honeymoon. You don't mind that food variety is narrower (the Greek-island restaurant menu is fairly consistent across the Aegean — and that's a feature, not a bug). Beach quality is paramount.
The cities argument
Italy wins overwhelmingly. Rome, Florence, Venice, Naples, Milan, Bologna — every Italian city has a distinctive identity, dense food scene, and walkable old town. Athens is the only Greek city that comparably rewards a multi-day stay; Thessaloniki is great but smaller. The Greek mainland's other cities are more functional than charming.
The islands argument
Greece wins decisively. Italian islands (Capri, Sicily, Sardinia) are wonderful, but the Greek archipelago has scale Italy can't match — hundreds of islands, a dozen of which are world-class, with a reliable ferry network.
The Italian island trip is one or two destinations. The Greek island trip is hopping.
The food
Italy wins on variety. Twenty regions with distinct cuisines, the world's most influential food culture, dinner-table consistency at every price point.
Greece is narrower and excellent at what it does. Grilled fish, octopus, dakos, mezze, fresh tomatoes, tzatziki. The repetition is part of the experience.
The cost
Roughly equivalent at the high end. Greece is cheaper at the mid-range, especially on the lesser-known islands. Italian cities run €130-€220 for a central mid-range. Greek islands run €80-€160 outside Mykonos and Santorini (which are punitive — Mykonos in July is luxury-pricing only).
The walkability and heat
Italian cities in July-August are 32-38°C. Walking three hours through Rome at midday is genuinely dangerous. Plan for early-morning sights and late dinners.
Greek islands have sea breezes and shade isn't an emergency the way it is in Roman streets. The walking is shorter (most island towns are villages) and the climate is more pleasant.
The wrong-pick costs
Going to Italy when you wanted islands: you'll spend the trip feeling exhausted by city heat and resenting the lack of clear water.
Going to Greece when you wanted history and variety: by day five you'll feel restless and the menu repetition will start to grate.
The combined trip
If you have 2+ weeks, do both. Italian week first (Rome-Florence-Venice or Rome-Naples-Amalfi), then a flight to Athens, then an island for the second week. The pacing works — you do the high-stimulation city week first, then the slow-island week.
For specific city neighborhoods see Rome, Florence, Venice on the Italian side; Athens and Santorini on the Greek side.