I've heard only use harley original plugs ?

How often should I replace the plugs?

I appreciate your feed back.

 

6r12's from HDMC. They're reasonably priced and designed for your engine.

 

Here is the cross reference chart http://www.harley-performance.com/ha...park-plug.html

I personally use Autolite. Cheap and I replace them every other year.

 

If you don't normally see oil burning on your plugs then use the Harley or Champions. I have a bit of a valve seal leak and the NGK Iridiums that I'm using now are great. They're more expensive, but they don't foul out like the others did.
You can throw away a lot of money experimenting on plugs that aren't designed for your bike.