Many CSS designers will tell you that designing your website in CSS rather than tables is better for SEO. Frankly, I haven’t seen that this is true. But it isn’t any worse either.
Whether you design your website with CSS or tables is largely dependent on preference and personal style. I think it may also depend on the website. Both tables and CSS have advantages and disadvantages, but I’ve seen top rankings with both.
CSS allows you to define page elements across multiple pages, which is very helpful and can save a webmaster a lot of time. By defining background color, font colors and sizes, sidebar widths, and navigation menu properties in your stylesheet (CSS file) you can make changes to those elements on every page of your site by updating just one file. That’s a huge time saver. But there aren’t any real search engine optimization benefits by doing it that way versus defining those elements for each individual page on your site. The best practices for on site optimization are still the same.
Tables are good to use if you have a page element that will exist on just one page, or perhaps a few pages, of your website. For example, you have a list of automobile models that you sell on your car lot; you can just wrap them up in a table to set them apart from the rest of your content. Again, there is no particular SEO benefit to doing this. It is simply a design technique.
In terms of SEO, there’s no real benefit to designing a website in CSS or tables. Tables are more tedious, but CSS has its own problems. Write too many stylesheets for any one web page to access and you’ll have load time issues. Since every CSS file is an external file that must be accessed by a web browser to show a page on your site to your visitors, each stylesheet slows the load time of your web pages just a tad while the browser looks for the information. For that reason, I’d recommend no more than two stylesheets per web page.
So which is better for SEO – tables or CSS? Neither. They are both good for SEO, but they each also provide their own advantages. Modern web designers make good use of both tools.