The stones were BL, because they were banned from UU. Now they are OU because of usage. The base forms are also OU because the tiering system doesn't separare the usage of base forms and mega forms.
Except Manectric, he was UU.
About Alakazam, I don't know, apparently the mega form is better. Smogon people keep changing their minds.
Mega Alakazam is better in a UU enviroment because of its speed and somewhat absence of priority in the tier. Mega dactyl (Speed tie), scarf users (The only common scarf user it outspeeds is Honchkrow, afaik) and honchkrow w/sucker pucnh are about all that can revenge kill it, I think.
LO magic guard alakazam is still more devastating offensively though.
Both are probably far too strong for the tier anyway.
Edit: I'm pretty content with the drops and feel like all would fair well, with the exception of Volcarona and Alakazam.
Just about nothing can stop Volcarona if it gets +1, right? It might not be the best in OU this gen but its certainly too strong for UU.