1. 80s for the improved writing, although most of the things that made Batman so "suck-y" started here. The excellent Breyfogle/Grant run counts as "80s"

2. 70s for the atomspheric stories, Haney's Brave & The Bold, but a lot of stories in this era were still really stupid
3. 1939 - 1950, because I like the Dick Sprang Batman who punched the villains while laughing and having a good time and the early Finger stories.
4. 2000 - Today; finally they are going back to a lighter approach and finally things like computer-coloring are getting mastered. But the early years with the Paranoid Psychoninja Batman were quite painful.
5. 1990 - 2000; the early years were good but then (see above, computer coloring) the stories became so gritty and somewhat soulless I couldn't enjoy them anymore.
6. 1950s - 1964; I am not really pleased with the "eras" the OP created, but these stories aren't as bad as many people made them, especially the early 50s.
7. 1964 - 1970; I do not really like the early "New Look" stories, yes they are more serious and are the start of the better "eras" but I don't like them that much.