reflector first, then RADAR, then AIS
Here in Nova Scotia we sail in fog or we don't sail much. EVERYBODY, from little fishing boats on up has radar reflectors. They are passive, which means they work even if you have no power and they don't cost very much. Besides, if you were involved in any sort of incident would you really want to explain to the SAR folks, or your insurance company, or the surviving relatives, why you were sailing in fog with a bag of tin-foil rather than a device tested to have a radar cross-section equivalent of at least 10 square meters?While everybody has reflectors, not everybody has radar, which is one reason why we do! The best reflector in the world won't prevent you from getting hit by a boat which doesn't have radar (Or isn't using it). Radar is also an amazingly valuable navigation tool. One important thing to keep in mind is that a good low-cost radar on a small boat will detect a big boat long before the expensive radar on the big boat will detect your little boat, which can give you a lot more time to alter course to avoid a collision.An AIS receiver is great if you only want to avoid the commercial vessels that are fitted with the transponders: All the other boats are invisible. If you already have radar, AIS provides great supplemental information (such as the vessel name so you can hail them!) and can show you vessels hidden behind headlands and islands. Also, if you have an AIS receiver (as opposed to the transponders that cost multiple boat-bucks) you are invisible on everybody elses AIS displays so, if you decided to get that instead of a radar reflector you are essentially invisible to everybody! So get a good reflector and don't forget the best collision avoidance system of all: Alert, capable crew on deck and watching!