If you had to pick just one, a good multi-surface cleaner or mild detergent is the most versatile. In a new home, you’re dealing with dust from moving, fingerprints on switches, random spills, and bits of grime left by workers or previous occupants. One decent cleaner mixed with water can handle floors, countertops, tiles, and many plastic or metal surfaces.
Choose something not too harsh, without a very heavy perfume. Strong smells might give you a “clean” feeling but can be irritating in closed rooms. With a bucket, mop, cloth and that one bottle, you can already make the place feel livable.
Later, you can add specialised products – glass cleaner, bathroom descaler, wood polish. But at the very beginning, you don’t want a cupboard full of bottles you barely understand. Start simple: one neutral, safe cleaner plus warm water, and do a full wipe-down of the most-used spaces. You’ll be surprised how much of that “construction smell” or old-house vibe disappears with just this basic combo.