I have Dior Show and I keep going back and forth about it.... I already have long thick lashes. I just like my mascara to make them look darker, fuller and more defined. I think the reason Dior Show looks so good is because the brush is really thick and fluffy, but that's also why it's so hard for a lot of people to use. I also find that when I use Dior, I HAVE to comb my lashes because they clump like crazy. This doesn't happen with other mascaras. And finally, Dior Show really irritates my eyes/ contacts. I heard that Blackout doesn't have the rose fragrance, so I might give it a try. Basically I like DiorShow, but I don't necessarily think it's the best product around.
Most days I use Bourjois Volume Glamour Ultra Black. It makes my lashes super dark, which makes my eyes pop. I've tried all of their mascaras and I've liked them all, but this is my favorite. IMO Bourjois mascaras offer the best value, because they're all dept store quality and only cost ~$12.
As for drugstore brands, I like Revlon Fabulash and L'Oreal Voluminous. The only thing I don't like about L'Oreal is that it dries out really quickly...