This is quite a question and one that I believe depends on what market you are in and what you need to achieve from your website, if you have a long term view and you are time rich but cash poor then Search Engine Optimisation (SEO) is with out doubt the way to go, you will not see dramatic results over night but in a few months you can get significant extra traffic by ensuring your site is set up properly for the search engines to crawl through and index.

If however you have a good budget and need to see immediate results then Pay Per Click (PPC) may be the best way to go, it will send visitors to your site from day one and with the statistics packages available you will be able to see the ads that resulted in conversions and the ones that were ignored by visitors.

This brings us to another important down side of PPC and that is that Ad blindness is worse than ever Comscore, the marketing research company shows that 16% of Internet users are responsible for 85% of all ad clicks on the web, so the vast majority of visitors from your PPC ads may well have clicked before, this may not be a huge problem if the sales levels are good but it is a disturbing trend.

It is important to have robots txt on your site, this allows you a degree of control over where the search engine spiders visit and what they report and store in their index about your site, this allows you to keep them away from commercially sensitive material or out of member only information if you have a membership area on the site.

Matt Cutts a leading engineer at Google has produced a video that explains the robots txt in more detail and and answes some questions such as

Why is my url showing up in Google when I blocked it in robots.txt? Did you fetch that url?

How do I make that url disappear from Google?

The video can be seen on Matts Blog at http://www.mattcutts.com/blog/robots-txt-remove-url/

This is going to be be of interest to any one who needs to know how to sculpt the page rank of their sites to ensure they are getting the most from the search engines.

This is an important part of search engine optimisation and implementing these changes on your site in the appropriate manor can help your rankings in the search engines.

One word of advice, do not go too over board with the robots txt file or you might find you have stopped the search engines indexing some important parts of your website and this will see you fall in the rankings rather than rise.

Asking if it is best to spend more on Pay Per Click (PPC) or Search Engine Optimisation (SEO) is a little like asking if you would like cake or ice cream, it normally depends on the circumstances at the time.

Pay Per Click is a great way of getting an instant boost for your company, getting the traffic in through the doors when the site is new so that you can test to see how popular the products or services you are selling are going to be, using relatively mall amounts of just a few hundred pounds you will be able to gage if people are interested in what you are promoting.

Once you know they are interested you can begin your marketing in full force, increasing your Pay Per Click budget and bringing in SEO for the site, Search Engine Optimisation is a longer term strategy than the PPC, but it does have the advantage of continuing to run even when you have stopped paying for it, although if it is stopped prematurely in a competitive market you can see the good positions drop quickly.

You are a little limited with the terms you can promote for with PPC as budget is always a concern, but with SEO you can promote for as many phrases as you like and you will find you are being found for phrases you did not even know were of interest to your visitors.

Rather than using PPC or SEO you should be using a combination of the two so that they complement each other as you move your marketing efforts forward, testing new markets with the PPC and promoting your site into the profitable niches using SEO.