I'm not looking to start a debate, but if you take advice from the "scientists," then traction-based extenders are the only way to definitively increase both flaccid and erect length. There are multiple credible medical studies that show length gains in the 1 inch range give or take over the course of 6 months or so. Obviously there's some deviation, but that's the gist of it.
Anecdotally, you may also want to consider that many men--myself now included--also testify to the efficacy of extenders. I have absolutely grown in length both flaccid and erect since starting in February, and some of my gains came very quickly--which is helpful in staying motivated. I'm still growing as we speak.
With that said, I suspect that "hanging" and jelqing may also increase length...there's just not the same scientific evidence to confirm the claims. Moreover, both of those practices are much more error-prone, which could mean safety issues and potentially injuring your penis. Given all the testimony, however, I believe men have lengthened their penises using all three techniques. Personally, I'm am most suspect of "pumping" gains, as the physiology of the penis doesn't really suggest that temporary pumping would permanently enlarge a penis--at least not in length. I suspect some men have probably made girth gains via pumping but I highly doubt long-term length gains from artificially bloating your penis for temporary periods of time. I also believe that much of the girth gains from pumping are more psychological than real, which is why it's so attractive to men looking for immediate gratification. There's nothing wrong with that, but having a temporarily-bloated organ doesn't mean it's actually been enlarged permanently.
I highly recommend that you stick with the science and get an extender--especially if you're concerned about length. If you go another route and get results, then more power to you. Either way, good luck!