you need both.
don't listen to the absolute retards in this thread.
extender is for long term length gain; essentially you stretch your penis and then the extender allows it to heal. it's time under tension that works this process so the longer the better. it's virtually impossible to injure yourself with an extender unless you are a basement-level IQcel
penis pumps are for girth gains. they work short term by filling the penis with blood and lymphatic fluid - this clears after a couple of hours but the blood flow remains for longer. Over time, your penis gets accustomed to the extra blood flow and engorgement. you then get bigger. this is a slow process and mostly works girth (unless you modify shit specifically for length by using a specific cylinder.)
with girth exercises and pumping you can damage your dick so it's best to go easy. bathmates and water pumping is a lot easier on your dick, but mostly it's about not being in a hurry and using too much pressure.
This and a few manual exercises will make your penis bigger and healthier long term.
