I'm thining about getting a book of puzzles, any recommendations? Any books to avoid?

Well, Chess: 5334 Problems, Combinations, and Games by Lazlo Polgar is excellent, if only due to sheer quantity.  While I've been going through it, I've found that similar puzzles are often grouped together, which helps me remember typical themes better.  You also might consider training on one of the free tactics servers to be found on the internet.

1. Do You think of tactical problems or composed chess problems?

2. How strong are You?

1. I guess I'm not sure of the difference.

2. On here I am in the 1500-1600 range.

There is a huge difference.

Composed problems are a kind of art. Except for the rules the positions have nothing to do with OTB chess. The focus is on beauty and brilliant ideas. If You are interested in this I would recommend "Solving in Style" by John Nunn.

Tactical puzzles deal with problems that will show up in real games. For 1600 player I think "The Ultimate Chess Puzzle Book" by John Emms is quite good.

I have ,,Enciklopedia of midlegames'' it's quite useful book for training and looking for the right move(s) or wining combination...

Chess Tempo have some good puzzles

Although I pour most of my energy into Tactics Trainer now, this book is my favourite.