If you have one week, no European trips behind you, and you're choosing between Paris and London — both are good answers. They are also dramatically different cities answering dramatically different questions. Here is the actual decision.
The fast answer
Pick Paris if your trip is romance-coded, food is the priority, you want to walk a lot, you're under 40, you're traveling as a couple, or you want the European-postcard experience.
Pick London if you're traveling with kids, English-language comfort is non-negotiable, you have a long museum priority list, you're a theatre or music person, you're 50+, or you want to combine the city trip with a few days in the British countryside.
Now the why.
Walkability
Paris wins decisively. Central Paris (the 1st through 11th arrondissements) is a 25-minute walk across, and the metro is for distance only — most days you'll walk 10-15 km without realizing it. The Seine is a constant orientation aid; the streets are at human scale; the cobblestones are real but not punishing.
London is bigger and walking-hostile in patches. The Tube is genuinely necessary across central London, and £6-8 per ride adds up fast (get an Oyster card or use contactless, which caps at £8.90/day in zones 1-2). The good walking is concentrated: Westminster to Covent Garden, Hyde Park to Notting Hill, Shoreditch east. Outside those, you're underground.
Cost
London is now significantly more expensive than Paris. A mid-range hotel in central London runs £200-300/night; the equivalent in Paris is €150-220. A pub lunch in London is £15-20; a bistrot lunch (prix fixe) in Paris is €18-25 and includes wine. Coffee at a café is £4 in London, €2 in Paris. Theatre tickets and museums largely break the trend (London's big museums are free; Paris's aren't), but day-to-day the gap is real.
Currency: Paris is Euros, London is Pounds Sterling. Both take contactless cards everywhere; cash is barely used in either city.
Language
London wins, obviously, if English-language comfort is the trip-maker. But Paris is much easier than its reputation suggests if you open with "Bonjour" before any request — see our Paris arrondissement guide on this. Almost everyone in central Paris speaks enough English to handle a restaurant order, a museum ticket, a metro question. The myth of rude Parisians is mostly a myth about tourists who skip the bonjour.
Food
Paris wins decisively. The bistrot prix fixe at €25 is the cheapest serious meal in Western Europe. The bakeries are still real bakeries (sourdough, real butter, the croissants are the croissants). Wine by the glass is €5-7 for something genuinely good. London's food scene has caught up impressively in the last 15 years — the new wave (Lyle's, Brat, Lyon's Corner House, the Sri Lankan and Pakistani scenes in East London) is genuinely world-class — but it's expensive and you have to know where to look. The default London pub meal is fine but not memorable.
Museums
London wins. The British Museum, the V&A, the Natural History Museum, the Tate Modern, the National Gallery — all free, all world-class. Paris has the Louvre and the Musée d'Orsay (both €17, both worth it) plus dozens of smaller specialized museums. London's free big museums make a 7-day trip with kids dramatically more affordable.
Weather
Roughly the same — both cities are at similar latitudes with similar maritime climates. Paris is slightly warmer and slightly drier on average. London's rain is famously light and intermittent; Paris's is more dramatic but less frequent. Both are workable year-round; both are best April-June and September-October. See our Europe in November guide for off-season planning.
What about both?
The Eurostar between London and Paris takes 2h20m and lands you in central Paris (Gare du Nord) and central London (St. Pancras). Round-trip tickets booked 2-3 months ahead are £100-150. If you have 7+ days, three nights in each city is the right combination for a first-time European trip — it lets you compare, gives you two distinct experiences, and avoids the "must see everything in Paris in five days" rush.
Where to base in each: in London, our London neighborhood picks point to Bloomsbury or Shoreditch. In Paris, the arrondissement decision tree walks through every option.