There are little differences. 4.3 (Without Sys Menu Update.) Is best imo because its compatible with the most up to date mods.
Where as ones below on 4.2 may have little updates. Only advantage I see with lower versions is the firmware, but it makes almost no difference since the firmware can be bypassed completely by removing STUB IOS's, and install & patch IOS 39 (AKA Trucha Bug.) To allow installation to allow more Wii Features.
Also 4.1 the only advantage with that FW is Mymenuify will work correctly, and Trucha Bug may already be present on the Wii.
With newer versions of FW on the Wii, you can still do this, but you will have to manually dig into information to have them work correctly, which is what I had to do with limited sources...