I have a theory re: who killed archie mitchell.
Peggy is far too obvious, because she's leaving soon, and she clearly was desperate to get the Vic back. But I can't see them ending the matriarch of the eastend's reign as a murderer, she deserves a bit more of a noble send off.
I think it was Roxie. With two motives: firstly, to avenge Ronnie, who clearly was the biggest victim of Archie's "evil" and secondly, because she knew that she was the only person who was consistently in Archie's favour- and that she would clearly stand to get everything of any worth on the will.
So this is how it would unfold: somehow, Ronnie would discover the truth, probably through Roxie accidently dropping herself in it. Not wanting Roxie to go down for murder, Ronnie hatches the plan to frame either Glenda, or the missing son Danny. They successfully get one of those two adequetly framed so that they go to prison, meaning that the viewers get an interesting solution to the murder, but don't need to see Roxie get arrested. Too many of the people with motives are too important as characters to go to prison, so this would seem the perfect way to reveal it, without having to lose one of them.
Although, this could be miles away from the truth. Janine and Phil are too obvious, Ian and Bradley are too wet. It either has to be one of the sisters, or an outsider... I did note that when the Vic re-opened Bianca was correctly able to identify the exact spot that Archie was killed in, despite having not seen the body... perhaps that's a bit too tenuous and I'm being a little pedantic. But apparently Bradley tries to top himself soon. My mother thinks it was Max. It's all just too exciting!