I just came up 287 from Williamsport and it's a beautiful drive in a sports car but I don't think I would take my 40' motorhome that way.
The road has many curves and some up and down "hills" that will slow you down quite a bit if you're in a hurry.
If you take 15 get off at the Liberty exit and turn left on 414. It will take you down into Morris and then take 287 for 12 miles to Wellsboro. There are curves and hills on that road too but it's not nearly as long as staying on 287.
I think that 15 is the better choice unless you want to take your time and enjoy "Penns Woods".
Mike