look like good games, but never played it, wich one should i buy?

Depends ;)

I prefer PR2, but it is a personal flavour. The graphics are better and if you don't care about multiplayer, PR2 doesn't have any, I would tend to go with PR2.

It is not based so much on fighting, although you can still do it if you want ;)

One BIG difference

In PR2 you do NOT battle lots of ships against each other, instead you choose with which ship you go first and in battle you can change ships.

Unlike in the first part were you can have bigger battles.

Some call it a draw back, other say it is a challenge ;)

The graphics are better in PR2, trading, citybuilding roughly the same.

Not sure, if you can do it in PR1, in 2 you can get your own cities.

And just in case I attached a review of the battlesystem ofPR1:

https://www.youtube.com/watch?v=3l52NmdW_es

oh well ended up not buying both of them