Le Marais is central and atmospheric, with cafés, restaurants and sights within easy walking distance. It suits travellers who want to be in the middle of Paris, although accommodation can be expensive and busier streets lively at night.
Saint-Germain-des-Prés is elegant and very central, with excellent access to the Seine, museums, cafés and restaurants. It is ideal for a classic Paris stay, but generally one of the more expensive areas.
Montmartre has characterful streets, cafés and famous views over Paris, with accommodation at a wider range of prices. Parts are hilly and reaching central sights often involves the Métro. Opéra and Grands Boulevards are convenient for shopping, restaurants and public transport, although the main streets can be busy.
Tip: Paris is large, so staying close to a convenient Métro station can be more important than choosing accommodation within walking distance of every major sight.