I subscribe to Ancestry.co.uk and have found they have a phenomenal number of parish record images that I haven't been able to see anywhere else, so I think it's worth the ~ £12 a month it's costing me.
I also subscribe to Findmypast, because they have an awesome number of parish record images too and once you have clicked on it, you've "bought" it, so if your sub runs out, you'll still be able to see the ones you have already looked at before.
What one doesn't have, the other seems to, so between the two companies, I have large areas of my family tree sourced from original images.
Familysearch is free and has a very good search engine, which I prefer to any other so I use that, then click to go to partner site (Findmypast) to view their images, which I am able to see because of my subscription. I also use Familysearch for sourcing people who emigrated to the US, because my 2 subs are UK only and Familysearch also have some very good US census and immigration sources. Also, they just got images from my local UK records office online this month, so it's all very good from my point of view.
The bad side of Ancestry is that many user trees are full of errors which get passed on like an infection, due to the ready acceptance by others of hints, without using any judgement. Take the family trees with a pinch of salt and verify or refute the info in them before accepting the hints.
The good side of Ancestry family trees is, a lot of people take photos of actual BMD certificates they have bought and they put them on the profiles. You can also find family photos. I found a photo of my uncle at work in the bell foundry, a photo of my great grandmother and a photo of my GG grandfather in the first hour after I subscribed to Ancestry.