Some twin engines use a single common crankpin and others use separate crankpins. Also the separate crankpins may go up and down together 360 degrees versus some that might be 180 degrees off from each other. With four cylinder engines you can see the same results, with two crankpins and paired cylinders setup in the same manner too. But some fours may have 90 degree separate crankpins though. But they could use 360 or 180 degree crankin setups too.

The three cylinder and five cylinder engines are pretty much forced into using a 120 degree or 72 degree crankpin orientation though. You can't pair up odd numbers of cylinders.

But the three or five cylinder engines would tend to be fairly smooth running, but a four with 90 degree crankpins would be fairly smooth too.