If just keeping one, I'd keep the 20 gauge. It seems the most versatile, without the appetite of the 10 bore.
If keeping 2, the 10 bore and the .40 caliber.
Here in CT . I can't hunt squirrels with a m.l. rifle larger than .36 caliber, and can't hunt deer with smaller than a .45 caliber, also can't hunt turkey with any rifle, but I can hunt turkey and small game with shot from a 20 gauge smoothbore, or deer with a single lead ball, 20 gauge and up.
Your laws and regulations may vary.