if you gotta choose between one or the other, always go reflective. hi viz can get swallowed up by city lights and car lights and low winter sunlight. reflective strips will always stand out when head lights hit it, particularly on your legs because they are moving.
my winter kit is hi viz top and black tights with reflective strips on them. my black overshoes also have reflective bits on them.
don't rely on it though, never presume a driver has seen you just coz you look like a giant yellow blob with reflective bits and lighted up like a Christmas tree. .
