The Piper cabin is smaller. It sits you lower on the seats. You are more comfortable with a higher seat like a chair. Back seat room is also compromised in the Archer. Two big guys can not sit side by side easily in either seat... at least not for long.
The Archer will go a few knots faster. Maybe 5-6. Not much difference on medium size trips.
The big difference I see is the handling of the Beech. It is quicker in roll. The Archer is sluggish. You work harder. The Beech is very stable in yaw, about the same for both. Pitch too.
The Sundowner has stronger landing gear. Trailing link. Better than oleo struts. There is no post in the middle of the Beech front window like the Piper. The view is 100% better in a Sundowner. Beech put more height between the glareshield and the top of the windscreen.
They both have the same engine. Parts are available for both. A Sundowner will be priced $30,000 less than an Archer. Buy the Beech. Use the money to upgrade the avionics.
It's my understanding that some Musketeers also have two doors.
The long ride from Toronto to Dayton and back by car has effected your brain. Beech made all these planes with no doors and the retail dealers installed what the customer wanted. That is why they all have baggage doors... so the ferry pilots could get into the cabin.