S&W 686 or the model 28

I want to start shooting bullseye with a revolver and own a smith 686 with a 4" barrel and a model 28 with a 6" barrel. I will be shooting with open sights indoors at 50' what would be everyone's choice of the two.

Both will work, but the extra sight radius of the 6" barrel is an advantage.  The 28 is heavier and should handle recoil a bit better too I suspect.  Use what feels the best to you.

The flat black front sight ramp of the Model 28 is easier for me to use than the red-ramp/white-outline that the 686s usually come with.

With target loads, either gun won't recoil too much. The 686 might feel a little more muzzle heavy than the 28, even with the longer barrel of the 28, because the 28's barrel is tapered and the 686's barrel is heavier and has the underlug.

Personally, I've found the bigger N-frame grip of the Model 28 to work better with my hands and gripping style than the smaller K/L-frame grip of the Model 686, but that's a personal thing.

If your 686 is a later model (-4, -5, or current production -6), it will be very easy to mount a scope. It isn't terribly difficult to mount a scope to an earlier model 686 (-3 or earlier) or the 28, however (though the available mounts either add bulk or clamp to the frame, or both, and can mar the finish).

I started by shooting a 28 single action with a target trigger and a target hammer. It has a great front sight. I have since switched to DA with a 686. I could do without the red ramp. But the 686 recently got me my first points.

I like  the extra sight radius of the 6" barrel on my M28.