It's been a long time for me, but I used to fish the Swift, Ammonusuc, Sugar, Pemigewasett rivers with great success. Just go out early and cover a lot of water. One of the streams out near Littleton / Lisbon area was packed with trout and I had a ball fishing a small hopper toward the shoreline as I waded along. I came back to camp with a couple of brookies and a rainbow where my girlfriend was just making coffee. Then we picked up some fresh butter and sugar corn at a farm stand, boiled it in the water from the stream at camp, fried the trout with bacon strips and cracked open a couple of cold ones to complete our "romantic" outdoor dinner. Things kinda worked out well with that girl - she's now my wife of 20 years and I'm still crazy about her!
Beautiful area up there, I hope to get back out there more now that we're back from the pacific northwest (another beautiful mountainous area).
I'd personally try to find out of the way freestone streams and C&R some native brookies. That being said I'd also love to float the upper Saco...