Through PP is not a way to go. PPH is further from the main entrance than DL. From PPH it is quickest to get to DCA through GCH.
From the DLH, the most direct way to either park is straight through DTD. It's very easy. You will pass the monorail station as you enter DTD. You can take the monorail into DL; it will take you to Tomorrowland, and will save you some steps. It may also save you some time if you don't have to wait very long to get on the monorail. However, I don't recommend you do that the first time you enter DL. There's something quite magical about going through the main entrance and walking down Main Street, and you'll miss that if you take the monorail.
An alternate way to DCA is to cut through the GCH, but it's not the shortest way to go. GCH has a special entrance into DCA that is intended for only for guests of the disney hotels.