I like the Monte, the M2 and the Affinity. I would choose 20 ga as well for weight. All three have basically the same action with the return spring under the forearm for the Affinity. The Affinity also doesn't come in a 28" barrel for 20 ga. The Comfort Tech stock on the M2 will help a little with recoil. Might choose Monte if you like wood and blue steel. You can get a slug barrel for the M2. The camo versions of the M2 and Affinity will be the most weather resistant. Child length stocks for the Affinity are less expensive.
If I wanted an O/U, I would get a Beretta or a Browning.
