Updated: Feb 9
There are many good Family History sites at the moment, the most popular and comprehensive of which in the UK are: Ancestry.co.uk, FindMyPast, MyHeritage and TheGenealogist.I have used all of them and can give you the benefit of my experience in the hope that it will help you with your choice.
In my opinion, for ease of use, number of records and number of members, Ancestry wins hands down. It's not the cheapest, and has a few features I'd like to see improved, but overall, I think it's the best.
It is often possible to subscribe free of charge for a trial period before committing to an annual subscription. Alternatively, libraries and local archives often subsciribe to Ancestry and FindMyPast and can be used on site free of charge.
An important point to remember, however, is that building your Family Tree with a particular site is not an all or nothing decision. Great strides have been made in standardising the way records are stored on these. So you can download your Tree and its associated records as a GEDCOM file, for example, and then upload it to any of the other sites. There are still some limitations with this - photographs etc. uploaded by individual members will not be incorporated into the GEDCOM file as they are simply too big - but these are relatively minor.
The same goes for DNA results. You might get your DNA sequenced by a particular site, but you can download the results at any time and upload them onto another site.