DB vs MDB

I am a newbie (very much so) and have a quick question, sorry if this is the wrong forum or if I have it all backwards, I am evaluating PHP at the moment. I had a look at some of the documentation and explanations of DB and MDB on the pear.php web site and came to the conclusion that MDB looks more functional and (generally) a better database abstraction layer, but DB has way more downloads and it looks like some of the other database "bits" are DB orientated. Can someone tell me what they think of the differences between DB and MDB and what they think I should maybe use? Regards, Densial.