Small stuff that comes off, gasoline - far more often than not. Doesn't really make sense to me to use anything more expensive, that takes more storage, that I have less of, takes longer out of my way to acquire, etc. It'll cut through grease well, without evaporating as quickly as brake clean so if I have some scrubbing to do, I haven't created a huge toxic cloud in the mean time, tho' I do still use it in a ventilated area.
Plus I usually use old gas that I would have had to dispose of otherwise, like that got dumped out of a 2 cycle trimmer at end of season. I keep a can labeled "dirty gas", and can strain it through a scrap t-shirt/whatever as needed, dumping into a parts washing tub.
If the part is something plastic and I don't want any residue at all on it, I might use gasoline first (depends on what it is) or just hot detergent solution instead, though for electronics/sensors, brake clean or electrical contact cleaner (depends on the situation). Brake pads themselves only get brake clean.
