If you can run to it, I'd suggest running two at minimum, a flasher (to attract attention) and a steady (to allow other road users to judge your speed and distance).
I had a Smart 1/2 w (it didn't survive my last off) and was well pleased with that, and the cateye one with an integrated reflector (which is nothing special, but ok). Keep the batteries charged, and make sure you don't inadvertently obscure the lights whilst riding (with clothing or luggage).