There aren't a whole lot of viking kits out there.
From what I've heard, one of the best is the old Esci 1/48 kit, I believe AMT reissued it with some upgrades about 8 or ten years ago. Not long after AMT also released a 1/48 ES-3B Shadow ECM variant.
Hasegawa has a 1/72 kit, but I think its getting a bit dated by todays standards unless they've made a new tooling.
About 5 years ago, there was a feature in FSM about a fellow in the Netherlands that superdetailed an S-3 in 1/48. He used the Esci kit and the result is a jaw dropper, so the Esci kit obviously has workability going in its favour.
Thats the sum total of my knowledge of S-3 kits, hope its helpful.
Good luck