LEDs have a much narrower field of view than normal bulbs - some LED lights get around this by having several LEDs pointing in different directions. Clipping an LED light to your body or helmet means that you can be sure that it will be pointing in the wrong direction for at least some of the time. They can be useful on dull days to get the attention of a motorist, when it is light enough to see a cyclist once you have noticed that they are there. There have been stories about drunk drivers hitting cyclists after getting mesmerised by flashing LED lights. I don't know if they are true.
Bicycle reflectors are cheap, robust and very effective most of the time.
Unfortunately, they are useless if a light isn't being shined directly at them. Fluorescent clothing is good for increasing your visibility during the day. At night dayglo colours are much less conspicuous - reflective clothing, and 3M Scotchbrite in particular, works much better. Don't assume that hand signals will be easy for other road users to see at night. Because the law says that you have to.