i have had both - cp for me was more of a keeper and i still have it - if you plan on playing it a lot it will get old - it's great for a collection of at least 6 games. the good is you have two very good challenging games right now.
usually ngg is easier to sell - but lately cp has been going up in value - it should as there aren't many made - everytime i think it's time to sell cp i go an play it - then say i can't get rid of it
good luck - either way you can't go wrong - thanks ed