Using whatever definition of "best" you want. And if so, what precipitated it? Personally, I found that being on anti-depressants worked wonders. I think a bout of depression is great for giving you some clarity and insight into life, but also tends to cripple your ability to do anything. So, being freed from the negative aspects but still having the insight fresh in my mind, I think I came up with (so far) all of my best ideas during that period of just-recovering-from-depression. Not that I'm advocating anyone go out and become depressed just because of writer's block...
God, hopefully I'm best now... leastwise better. it would suck if my best was in the past. Sometimes I feel certain ideas and moods slip away from me cause as a person ( not just writer ) I've changed and continue to change and I'm wistful for that past view. But there's no stopping that.
I'm too young to have produced my best work, and I think this is true for a lot of members here. Talk to me in 20 years.
So far the current stuff is the best - although I'm not that old (late twenties). Personally, I fid the more time I spend with the craft, the more I'm able to do with it, but also that my view on the stories change. I'm in an interesting position in that I'm working on a concept I came up with when I was just starting university about ten years ago and just came back to last year. When I first came up with it, it was very much a political polemic meant to make a political point. Coming back to it, the storyline hasn't changed, nor have my politics, nor have the political parts of the storyline - but I'm far less interested in the idea of a political book. Now it's very much about the characters, their struggles with the nature of truth, and the idea of fighting the steamroller that is history (my overarching theme is that choices made in the past pile up, and the more they pile up, the more radical the action required to stop the wheel). My villain started out as the embodiment of everything I couldn't stand about the political left, and specifically the people on the left who get so ideological that they become the sort of bigots they think they're fighting...and she hasn't really changed, but now I'm far more interested in her as a parable about how even deeply good ideas (like tolerance and women's rights) can become dangerous when taken to the point of militant extremism. I care less that she's leftist than that she's taken her ideological beliefs so far as to legitimize inhumane treatment of anyone in her way - and that's unfortunately a commonality shared as much by people who agree with me as by those who agree with her.
I guess this is similar to what I'm going through--I keep revisiting ideas I had years ago but feel like the new ideas I have now aren't as good. But as they say, confusion is the first sign of learning, so maybe this is just a function of the actual writing process being harder than just having a good idea and not doing anything with it. 1% inspiration and 99% perspiration, and all that. Anyway. It would be nice to recapture the feeling of inspiration, but who knows--it's not like anyone read anything I wrote back then, so maybe it was all crap. Hopefully the intervening years have improved my actual writing, if they haven't produced any flashes of brilliance.
I have a feeling this will be my answer until I die. Ideally each new creation should be better than the one before it.