I'm not sure I can do a decade by decade breakdown, but here's a two part breakdown:
20s - 80s I will watch almost anything knowing that they are almost always enjoyable. almost all my favorite are from these decades, with the fewest from the 40s but there was a lot less horror being made then. If you twisted my arm and strapped a heavy weight to my ballsack then my top five decades would be:
30s
70s
20s
80s
50s
90s through today - there have certainly been some great films made but overall the genre has gotten a lot less interesting with more cookie cutter crap produced. There have been great films in each of these decades but none of the decades stand out for me. Anything I said under torture at this point would just be meaningless mumbo jumbo.
This is so tough. On IMDB I was always tempted to contribute to these threads, but I almost always chickened out. But, just to make an effort here, I'm gonna go out on a limb and try to at least clump my favorite decades in groups of three. The order within each group of three could possibly be changed, but right now I'm gonna say...
Top three decades:
80's
70's
30's
Middle three decades:
60's
2000's
2010's
Bottom three decades:
50's
90's
40's.
The 20's is a floater for me, personally. Maybe between the top set of three and the middle set? There were some absolute all-time classics made then, of course, but it is hard to really enjoy them anymore... very tough call. By the way, the 50's is also a really tough one, I was really unconfident about where to put it. It is sort of comparable to the 80's, just in the sense that there was such a quanity of horror/scifi being made, but so much of it was pretty low quality. But, of course, the same could be said about the 80's, which I put on top, soooo I guess it's just my own opinion, not objective.... I feel bad putting the 40's so low, because there were a few gems, e.g. The Wolf Man. But... I mean, come on, where else could I put it?