Best site for high quality challenging tactics problems?

[Alobar]

Ive done like 4K of the problems on chess.com (paid the monthly) and they are pretty good.

[Gorgonian]

If you have a premium account on chesstempo.com (ridiculously cheap) you can make a problem set with only 4 and 5 star problems, if you want, too. That would help with the quality.

[Gorgonian]

And yes chesstempo uses engines to check the solutions. In fact, the site uses engines to find the problems in the first place, so the assertion that "this proves they don't use engines" is ridiculous.

Putting the problem's rating as evidence that it is "supposed to be easier or harder" is disingenuous, too, since the ratings are a direct result of which players solved the problem and which players failed it. So if it has a lower rating than another problem, thus far it has indeed proven to be easier. That could change over time, though, as more data is collected.

[Vempele]

Originally Posted by Gorgonian

Putting the problem's rating as evidence that it is "supposed to be easier or harder" is disingenuous, too, since the ratings are a direct result of which players solved the problem and which players failed it. So if it has a lower rating than another problem, thus far it has indeed proven to be easier. That could change over time, though, as more data is collected.

It's only easier because more people randomly stumble into the right move and/or realize that the main alternative, though good, isn't good enough for +1.75. As for how hard it is to fully work out the solution - they don't even try to measure that.

[Gorgonian]

Originally Posted by Vempele

It's only easier because more people randomly stumble into the right move and/or realize that the main alternative, though good, isn't good enough for +1.75. As for how hard it is to fully work out the solution - they don't even try to measure that.

That is correct. One of the downsides to the system used, but it's still a pretty good system. People can randomly stumble onto the right series of moves in an actual game, too.

[NajdorfDefense]

chess.com TT as others have noted.