As is the case with many things in life, the answer here depends. Boilers and furnaces heat up homes very differently, and they also start at different price points and come in different sizes. All of those are factors that can make each of them a better fit for different situations.
For example, if your goal is to warm a small home and you want to keep your budget as tight as possible, a furnace is the better option. Modern furnaces can be incredibly small, and they start at a lower price point.
If you have a large home, however, boilers are a good option. They are more energy efficient; some people find them to be more comfortable since there is no hot air being blown around the house. And a boiler can double as a water heater to heat up bath and tap water.
Boilers can also last for a long time. With proper care from a boiler service Surrey team like this one, a boiler can last 20+ years before needing to be replaced.