Out of the following tools which would you say has been the best all round experience for building a website for free.
For free, or for a very low price, I would add the following hosted website builders to that list:
1. Wordpress.com
2. Microsoft Office Live
3. Website builders from some of the hosting companies, e.g. Instant Site from 123-reg
4. GBBO (Get British Business Online with Google Sites)
How free the tool really is
One other thing to consider with free, is freedom of choice. Most sitebuilders are based on proprietary systems which make it difficult for you to move your site away from a service, so check exit strategies with different services.
The notable exceptions include wordpress.com which obviously use wordpress, but a customised version of wordpress, so to get something similar when moving away you would still have to apply those customisations to the default wordpress system.
The other notable exceptions are the sitebuilders used by some hosting companies. They might not be open source like wordpress, but some are white label versions of the same software (e.g. parallels sitebuilder), which does give you some freedom to move to another hosting company using the same system.
I noticed a music related website in your signature, so for music related sites I would also recommend looking at a myspace page, perhaps in addition to a normal website.
One other thing to consider with a lot of hosted website builders is the server location. A lot of the services are US-based, which isn't such an issue for .co.uk domains but might cause other issues if you have a .com domain (i.e. google thinking that you are US based, thus not ranking you so highly for searches in the UK).
A final consideration on exit strategies is what happens with domain names, if they are originally registered with the website builder service. I personally would recommend that you purchase the domain yourself from an established domain name registrar like 123-reg, and then point the domain at the website (e.g. by changing name servers or DNS records). Services like wordpress.com (at a small yearly charge) and Microsoft Office Live allow you to do this, so I'm guessing quite a few of the other services allow this too, if you look closely enough.