When flying in from another country into Paris you have the option of taking the train, or getting a taxi. If you have more than one small bag, and there's more than one of you, I would recommend taking a taxi to your hotel. It's no fun dragging your bags through the subways. If traffic isn't especially heavy you should be able to get to Paris center for about 30-40 EUR - and it's totally worth ever penny!
For getting around Paris, for me i thought it was worth it for a few areas that would have just taken a little to much time to walk or it was too cold - when you're traveling with one or two people it only ends up costing a couple Euros per person anyway. If convenience is a priority for you then i think the taxis will serve you well, as they did us.
TAXI STANDS: Be sure to look for your taxi at the designated stand, otherwise, they will not stop for you.