I would say GCH!

The park will be open long hours during the summer so you will have plenty of time to walk back and enjoy the pool and/or lobby and then head back to the parks to use your fast passes in the evening. The GCH is much smaller than any resort at WDW - so enjoying it doesn't take as long!

Also, you will be amazed at how close and convenient the hotel will be to BOTH parks - there is actually an entrance into DCA from the GCH! And DL is also a few minutes away.