Here's a summary of ways to get from CDG to Paris:
Getting to Paris from the Airport
As for the OP's question concerning shuttles, I haven't taken one for a while as I was having such mixed luck with them (having tried a few different companies). Someone posted a while back in this forum about a company they liked but I don't remember which one. Private shuttles seem to be a bit more reliable than the shared ones. Otherwise, if public transport isn't convenient, there's always the option of taking a taxi.