A decade or so ago I would have said Coronation Street but the bad writing is starting to lead to some equally bad acting from previously reliable script savers. Barbara Knox, Beverley Callard, Kate Ford to name just a few off the top of my head. All previously very good actresses that seem to be forgetting how to act as each year goes by. (And before anyone puts my head on a stick for mentioning Kate Ford being good, I thought she was great in the Karen/Steve/Tracy stuff

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I've never thought the EastEnders cast were anything special. Downright laughable in some episodes and scenes I've seen but the ones that I am familiar with in other shows have been good - Ross Kemp and Diane Parish being two I can think of straight away. I don't think the writing tends to do the actors much good though, for the most part it's either look solemn, cry, shout, glare or look threatening at somebody. There seems to be little else in the way of talent required. Sadly Coronation Street seems to be going the same way at the moment.
I've seen very little of the other soaps, bar Emmerdale, so can't really speak for them. The little acting I've seen from Doctors and Hollyoaks though has not impressed me much at all. So right now I'd say Emmerdale. Some of the cast still continue to surprise me with their ability to switch between drama and humour and the cast are able to do their best with the occasions when they're given horrendous scripts and still manage to play them convincingly.