Hi Nellie
I have no experience of Origins, but as far as Ancestry is concerned I have found my year's subscription very useful in order to get census info on all my ancestors from 1871 to 1901.
I don't have many ancestors in Wales though, so the only bits now missing for me are some chunks of 1901 which I've filled in from the government site, which has a better index anyway.
I doubt if I shall renew at the end of the year, but that is because, prior to 1871, my ancestors didn't move about much, so buying census images for a few single counties on CD provides pretty well all I need on that score and there are some very good ones about. (I'm particularly enthusiastic about Gordon Beavington's although he only has 1851 and a few 1891's at present)
As for BMD - Ancestry only has what FreeBMD does, apart from deaths after about 1984 and I've only found that useful once. I've found 1837online most useful to fill in the gaps from FreeBMD.
Ancestry also has quite a few other databases in their UK collection but I've never found anyone in any of them.
I think, if you do a trial subscription, that you have to carry on with the one you started if you carry on at all, rather than change to another one.
Hope this helps - I don't know how typical my experience is, but that's it - it was very useful indeed for a limited period but only for censuses

Regards
Angela