Originally posted by agentreno
I've tried them all and Chess Tempo is the best. I'm considering subscribing there for the extra features, like analysing your worst tactic areas and selecting to solve tactics for that theme.
Chess Tactics Server rushes you by penalising you for taking too long, which I really don't think is a good thing.
Finally Chessimo seems to be limited to mate puzzles, at least it has been so far for me after using it for a month.
I think for tactics, CTS and Chess Tempo add up to an almost ultimate combo, no need for other software there, except a good engine to analyse your mistakes or check out sub variations (that you yourself have calculated beforehand).
but for endgame puzzles and drilling them until all the patterns sink, chessimo is very good, I think. at least I don't know of any free websites or other software that has such an endgame puzzle set.