Many of those websites are doing illegal service by providing free ringtones so if you don't want to get involved with law matter I suggest you to take the ringtone service with subscription fee. Usually ringtone website that charge you with subscription or membership fee already has some kind of agreement with the copyright holder of the ringtone that they distributed.
If you live in a country that doesn't really concern with the copyright issue you can use the free ringtone service which mostly illegal. Oh I almost forgot, I suggest you to join some mobile phone forum because usually members of those forum provide you with unique ringtone that they created for free.
Don't forget that usually your provider also provide you with ringtone service and usually this way you can get the latest top ringtone easily but based on my experience it is cheaper if you join with online ringtone services. Well, just follow the way that suits you the best.