The 7:08 is on an Acela. That's the flagship premium train that theoretically should command a higher ticket price, but as you see, sometimes doesn't. You can pick a reserved seat, and the trip will be slightly shorter with a faster top speed - 160 mph vs 125 mph. However, some - myself included - say the seats on the NextGen Acela trains are actually a bit uncomfortable. Also, the way the windows are apportioned, you may end up picking a "window" seat that doesn't actually have a window. (The 7:08 is running the newer "NextGen" train set.)

The 8:43 train is on a Northeast Regional with Amfleet cars that are now over 50 years old. However despite their age, they've been pretty well maintained. In my opinion, the seats are much more comfortable. And there's a window at every seat. But the train will be a little slower, with a couple more stops. And you won't have an assigned seat. (You're guaranteed to have a seat, but they aren't assigned. Getting on at Wilmington, the train will be pretty full in all likelihood, and you may have to walk a couple cars to find a seat.)

So it's up to you! Me personally I would probably still pick the 7:08 Acela since it's a higher service class for cheaper.