RE: Which sail for S-Type 104
In Sails around that size range, the Gator is an excellent match to the ST104 in choppy, fast freemove type conditions and the 5.0 would fit well with your existing S-2 5.8m.
If you wanted to go more into the wave sail range, the Blade 5.3m is probably the best choice, it delivers a lot of locked drive (for a wavesail). The Renegade is fun and very durable sail, but with a very soft feel, which is not so matched to the freerace/SuperX character of the ST's.
Cheers ~ Ian