solving tactics on internet (chesstempo) and on book? which is more effective ?

See, there are at least 100,000+ puzzles on the internet, but why are people still publishing tactics book ( like The Giant Chess Puzzle Book etc.) ??? May i get the answers from some of the experienced players??? how you all improve your tactics to a whole new level ( like breaking 2000 )? consider buying one puzzle book... but realizing there are free puzzles on internet... HELP ME PLSSSS!!! 

Some players argue that books are better, because it forces you calculate all the variations right up until the end.

With internet puzzles, because they are timed, players tend to make the first move that comes to mind if they are not sure of the answer.  Then, if you happen to "guess" the correct answer, the following sequence of moves may (or may not) become clear to you.  Ideally one should always calculate the best possible lines and avoid playing "instinctive chess".  Thus internet puzzles could create bad thinking habits.

On the other hand, some players argue that timed internet puzzles improves one's ability to recognize familiar patterns quickly, which could be critical in a game where you are running low on time.

So my guess would be that a mix of both would prove most effective in the long run. 

A book like Magic of Chess Tactics or Dvoretsky's School of Excellence 2 will tell you why a move is good and what methods to employ in a particular situation.  Some positions aren't even side to play and win but inferior side to force the draw, play and equalize, transition into a better endgame, etc., so it reflects more realistically a practical game play, because in a real game you won't always have a play and win tactic.