3 factors and why?

Title, because that's what on top of the SERP ad.
Content, because that's what on the text ad
Refresh content regurarly, because that's what make the site 'live' and loved by SERP...

There is no correct or wrong answer. Everything is important.

1. Content - No content, no traffic, no money. Nothing to optimize.
2. Titles - Explain what is this content about.
3. Backlinks - Indicate that site is worth reading.

In case you didn't notice, there are already two other questions asking the exact same thing on the SEO Talk Forum front page.

Originally Posted by seozero

There is no correct or wrong answer. Everything is important.

1. Content - No content, no traffic, no money. Nothing to optimize.
2. Titles - Explain what is this content about.
3. Backlinks - Indicate that site is worth reading.

I would have to 100% agree with seozero's list, this is exactly how mines would be

And fresh content.

Meta Tags
Content
Design

content
links
and web site age by google not by whois
That is my own opinion on all that.

For me, all the process of doing SEO is the most important...

1. Title tags
2. Optimized, original content
3. Quality, relevant backlinks.

1. Title - Has to be snappy something people will remember.
2. Design / Content - Needs to be well designed with a balance of good content.
3. Reliable - Good amount of back links, great sources, and EXCELLENT! load speed and up time.

- more links
- keyword density
- page rank

I wanted to add Alexa Rank but no more room.

I agree with SEOZero.
And the most important thing is three factors works very well if you go for consistent link building process.

I can only say one factor that is very important for me as an SEO, and that is the traffic that I receive, the visitors... Though those stuffs that you have said can be the ways on how they could see my site faster, I still try to focus on my visitors. Make content for my products and services for them, do ads and articles for them to read and improve my products and services to have more returning visitors.

for me the 3 most important factors are site content, keywords and relevant backlinks!

1. Planning - Without a plan in place you have no idea if you are successful or not.
2. Analytics - If you don't analyze your traffic and visitors you have no idea if your plan is the right one or not.
3. Testing - Using your analytics test various tactics and techniques to improve your overall ROI.

All rest is just throwing crap on the wall and hoping you magically find the thing that works for you, your site, and your visitors. And then when it works, or doesn't work, you don't know why and can't repeat the process.

For me, id say:

-Links
-Content
-Page Titles

On Page
Off Page
Social Networking.
Most important factor in SEO....

Originally Posted by ciplseo

Off Page
Social Networking.
Most important factor in SEO....

Neither of which are ANYTHING to do with SEO

Originally Posted by lindamoodbell

Title, H1 and Img Alt Tag

Just guessing then?

BTW there is NO SUCH THING as an alt"tag"