It has been my experience with the "Believers" is that engaging them really does not work.
Usually, like say with the LDS, they are sent to schools and have a list of open ended questions they give you.
Like, "What would it take YOU to believe in ____(you fill in the blank). The best way is to ask their questions to THEM before they get a chance to ask them of you.
So, "Let me ask you a question....What would it take for you to reject your religion or your religious beliefs?"
Remember, most of the people have been socialized or conditioned since they were infants on their "beliefs".
But be careful of being "nice" or "respectful" to these types.
They have been conditioned to believe that YOU or YOUR BELIEFS or wrong. And that their beliefs take are the ONLY beliefs that are right or correct.

I think it's fine, indeed admirable, to respond to theist propositions, propaganda or legislation. If someone starts it, I have no problem finishing it. Bring it on!
That said, it can be obnoxious to preach, as you say.

My Anatolian rabidly barking at them usually makes them not want to stick around too long. All my experience with Mormans and JWs is that they're trained to reject anything that contradicts their beliefs, even if you did have an impact on them you'd never know it. They'd never show the slightest inclination to your face bit maybe they'd reflect on it later.

I don't really feel the need to engage in a conversation with the JW or any other person who is trying to share their faith. I've only seen the JW come to my house twice. One time they didn't get far from their car before they scrambled back into their vehicle. They probably heard my dog barking. The other time I saw them come up my sidewalk, I opened the door and said I wasn't interested, they turned around and left. Don't feel the need to try to "convert" theists or tell them how "wrong" I believe them to be. Who am I to do that stuff? I'm not the prophet or preacher of atheism/agnosticism. I keep to myself my personal thoughts about things. If someone asked, depending on the scenario, I might share what I believe. I learned long ago that I need to pick the battles in which I will fight.

I don't feel the need to engage anyone about their beliefs. You believe what you believe, I'll believe what I believe, and we'll both be happy. As for JW's I just tell them I'm not a believer and "Thanks, but no, I don't need the literature".

I had a similar experience when two older JW's came to my door. They introduced themselves and then quickly asked me if I thought the Bible was relevant in the world today. I said no and as he started the next part of his speech he realised Ididn't say yes and had to back peddle. It caught him completely off guard and he asked the question again thinking I didn't understand it. We then talked for a few min. as I explained that I truly did not find the Bible relevant in any way. Then I thanked them for stopping by and they left. I have a feeling I may have been their first "no" answer to that question as I live in a very religious part of Florida. I also have a feeling I won't be seeing them again.

Thanks for all the input guys I see the consensus is to engage. I think they just caught me off guard as I didn't notice them approaching the door. I think in the future I will open with the reverse questioning ploy of 'why do you believe what you do ?'. The main reason for the post was I was really supprised at how young they both were as you usualy see older JW's or one older and one younger. I just wanted to 'save' them I suppose lol

My belief in questions is, if you aren't prepared for the answer don't ask.

For JWs or LDS, you didn't go looking to engage them on the subject. They are out there trying to save souls, presumptively, but they are being manipulated to generate revenue for their respective churches. The church is counting on their naivety and unquestioning belief. Where's the harm in presenting alternatives?

They are happy to use freedom of speech/preach to offend you with their irrational emotional belief, so a good response 'when' they come back is ask ''Why do you belief when there is no rational evidence on which to base it'' debating is not preaching

If conversation about what you believe is offensive, then they had invited you to engage. They were not interested in debate though, I am sure. I doubt they are equiped by their faith training to do such. When I have had discussions with Witness's and others, they usually return with standardized objections around what you have said, regardless of it saliency to what you have said.

I'll offend anyone & I pretty much do

you can't change stupid mate, i would quit while your ahead

I would have given my explanation and reasons.

Yes - I think when you "discover" the truth, its natural to want to share your beliefs, to enlighten others. But what I have learned is that many are locked into their beliefs and no logical argument will open their eyes.

I generally do my best not to offend anyone. I am not always successful, as is
evidenced by many of my comments here.
However, if you come to my door to "enlighten" me regarding your beliefs, I'm probably going to say a few things that end up offending you, even though my intent is to have
a rational exchange of ideas.
I find door-knockers to be highly offensive. They get what they get.

I don't feel bad for giving them reasons when they knock on my door. They approached you. Most of the time I just answer the door tell them I'm atheist and close the door.