I'm note an expert on this, but my experience and what I have read seems to say that once you have the keywords in the domain name part of the URL, you probably don't need them anymore in the remainder of the URL. So personally I would go for:
Also, the second one will look a little bit nicer when it appears in the SERPs and therefore MIGHT have a higher click through rate than a longer URL.
(However, I BELIEVE that google might take liberties in how it displays your URL - along with your page title - so it might show just a short URL anyway. Hopefully others will chime in on this.)
I'm a big fan of USABLE urls. If the user can type it and remember it, and it uses the keywords, what can go wrong?
To that end, I wouldn't use a .php suffix. I'd set up .htaccess to set php to serve non-suffixed urls. I'd drop the www. I'd also drop keyword repetition. I'd go with: thebestyellowball.co.uk/large
Some folks here have reported recently that they have had trouble ranking suffix-less urls and had better luck when the url had a slash at the end. Because of these reports, I might modify my advice a bit (although it pains me from a usability standpoint): thebestyellowball.co.uk/large/
Lose the folder detail, especially if the site has multi-faceted navigation.
Especially lose the .php extension in the URLs. You will be able to massively improve the efficiency of your rewrite rules as you will NOT need any -f and -d "exists" checks.
Don't end URLs with a trailing slash unless they are for folders or for the index page in a folder. The recent report about problems with some sites was for URLs with path ending in .com; maybe there's a problem with that one scenario.