As for where to fish, for one, note that significant sections of the stream are ATW's and off limits to fishing till opening day.
That said, the special reg areas are open, and they are the best sections of stream anyway.
Trophy Trout Section - From confluence with Elk/Pine in Coburn downstream to the wire downstream from Swift Run. The access areas are Tunnel Road that follows the stream downstream from Coburn and then dead ends. You can fish along it or walk down from there. Or at Poe Paddy State Park, where you can walk down or up or through the tunnel. If you go through the tunnel and down, you hit the wire in a few hundred yards. A nice full day is to go through the tunnel and up, about a mile of water and you'll come right back to the car. But you'll have to cross a few times so if it's high that could be out.
ALO C&R stretch - from the wire down from Swift Run downstream to the mouth of Cherry Run. Access points are from the top at Poe Paddy State Park (through the tunnel and down), or from the bottom at Cherry Run (and walk up). A nice hiking/driving/biking path follows the stream along the north side. This is my favorite stretch, I think. 2-3 miles of roadless big water in a gorge. Big long pools separated by pocket water riffles, and splits into islands in several places where a "smaller stream" experience can be had.
Note the driving time from Coburn, Poe Paddy, and Cherry Run access points are very far apart by car. The geography of the area means you have to go WAY around to get to the others. If you're at Poe Paddy and want to go to Cherry Run, it's a 2-3 mile hike OR an hour by car, lol. I've always been partial to the Poe Paddy access point because it opens your options up. You can go up, down, or through the tunnel and up or down (going through that tunnel lands you well over a mile downstream of where you just were). It's also the heart of the gorge and just beautiful.
But frankly, the decision is made for most by where they're coming from. If from the north (Lock Haven, Jersey Shore, etc.), Coburn is by far the closest, and it's a hike to go anywhere else. If from the south or west (Milroy, Reedsville, 322 corridor, etc.), Poe Paddy is closest. If from the East (Mifflinburg, Sunbury, etc.), then Cherry Run is by far the closest access. From State College, Coburn and Poe Paddy are about equal in time, but Poe Paddy is a lot of dirt roads.
Compared to the streams you mentioned, Penns is bigger and has a lot more bugs (though Fishing Creek is no slouch, of course). Bigger fish. But it's more temperamental. Meaning, the fish don't feed as constantly, and if they aren't on the feed fishing can be very difficult indeed. Hit it right and it can be fantastic. It comes across as more "technical" for that reason, you have to meet the fish on their terms to be successful. It's my favorite of those 3, but its 3rd for sure in average catch rate. I just like the size and setting and like a challenge. It always seems to throw something unexpected at you.
Also, in terms of flow and color, Penns is among the first to come up and muddy up, and the last to clear. Flows through a lot of valley farmland before it gets into that gorge. When planning a trip well in advance, a plan B is required.
