To answer which code language is best for Search Engine Optimization efforts, as the other two answers to this original question stated, HTML is the best.

For all the reasons this particular answer stated is pretty spot on.

I'd like to add in a little info. here now about best-use strategies on how to make the most of your coding optimization.

Lets start off with one little known clue that the ratio of code to content is an important factor. See, Search Engine bots or spiders read code in different ways. For example, you can cloak or hide links if you code them in Javascript, but if you code them in HTML then the spiders will crawl and index that link unless you the "rel=nofollow" attribute to your <a href> tag.

What's the point? Well, using code that is clean, easy to read, and fairly logically laid out makes the bot/spider's job easier in a sense. In reality, it'll just skip over certain segments of code that contains errors, is too complex, not supported, etc.

In the end the code, while used to present the page itself is really just used as a tool to enhance your content in the eyes of the spider/bot. In other words the spider will read your <p>Text</p> regularly. However, using additional HTML tags we can convey importance or less importance to items by selectively using different tags like bolding, and obviously the H1, H2, H3 tags, etc.

For this reason, you want to keep the ratio of code to text content at around 60/40 (60% code, 40% text). I say this because once you start getting to the point where every other word is styled you're becoming the "boy who cried wolf". The spider bot will start to devalue your styled words due to the ratio of styled words to un-styled words, etc. Basically, it is smart enough to see that you're over using styles to convey importance.

You can help get around this in certain ways by using CSS. Make sure to create your CSS file as an external file and link it to your HTML file while editing. This way you can style your content without the worry of losing that content/text ratio. However, you still have to pay attention so that you don't over do it.

You can use the same technique to store your javascript in seperate files if you need to use it.

Now as other's stated you can use PHP or ASP for example. In fact, I use php quite often for their library include features which, for example, all you to create a navigation element that you simply include on each page. It makes editing many pages at once just a bit easier. These pages are indexed and crawled the same if they're static. Again, a static page is one that is not generated on the server side. (ex: site.com/order.php?cart=2) or something like that. However, if you create a normal HTML page and save it as .php on a server that supports PHP you're good to go.

Some of the cons to using HTML are actually the very reasons we've already discussed. The fact that HTML pages aren't created on the server side means that you can't use HTML pages in the same ways you would ASP.net or PHP for database purposes or for other dynamic content purposes.

While you can export CSS to an external file to cut down on that code/content ratio CSS is not interpreted by all browsers the same. This can be a pain when ensuring that a page appears the same on many different browsers.

HTML is very limited, if not basically crippled, when it comes to logical programming where you need to decided things (ex: If, else if statements). HTML is also not the tool to use when needing to perform complex tasks or calculations.

Finally, these last few points, when put together pose a big problem for online shopping carts if you're looking to start your new online business. However there are many shopping carts that will now allow you to produce your entire store and export static HTML pages for every product, product category page, etc. This ensures that all your products will be indexed. An excellent example would be the shopping cart, X-Cart.

Just remember that HTML is excellent for presenting textual content. For that reason textual content remains one of the, if not the most important factor for on-page search engine optimization.