HS-6 Easy on the gun, good dot movement, easy to find cheap.
Depends on your gun though. Mine is a Bedell shorty with popple holes.
Shorty with no holes HS-6, 3N37, N350.
With a full length gun Silhouette, True blue, HS-6, N350, 3N37 or a few others depending on how yo like it to feel.