Oxbridge Essays, just read their through their company website at http://www.torg.co.uk/
and ask yourself whether some of the claims made are really believable? Read through their site and make your own call.
We are not allowed to make recommendations here but pls do read through various threads and you will find some of the sites you have listed mentioned. Go through these threads.
Pls log onto all of them, read through their website, talk to them and make up your own mind.
Another thing - do not go for low prices and keep in mind that good writers demand real pay.