Normally, I'd absolutely advocate for the Battenkill. You have the Battenkill, Mettawee and Wallomsac all within a half hour drive of one another which means a long weekend would allow you a day each on three good trout streams.
Having said that, this time of year also brings the worst of all fly fishing blights that the Battenkill sees: the out-of-town canoeist.
If you get the chance to head up later in the year (later September through end of season) I highly recommend it. The long drive is tolerable when the colors along the long road start to hit their peak. And there is just something amazing about fishing the Battenkill with a brilliantly bright Mount Equinox as a backdrop.
Of the two remaining options, I'd go PA but I have an obvious bias toward wading New England waters.
not sure exactly where you want to go, but two weeks ago i went to northcentral pa (route 14 north of williamsport) and got a little fishing in. had some decent luck with stocked brown trout in local streams. caught 3 12 inchers in 2 hours first thing in the morning but saw many 20+ inch trout in the streams that weren't biting.
yeah, I'll hit the au sable. they just had their big hex hatch. large fish rising. but it should be fun. the canoe race is happening on the 25th this year. SOOO, I'll be there for that. think I'll just head to the North Branch, which is actually my favorite part that day.
I really want to go to the UP, there's a stream that I need to do more exploring on up there. but thats anotyher 350 miles of roadway. twice the distance.
I did the PA thing this spring, Penns creek. I like it there.