Water/Elect grants you access to Shard of Glacier, which nearly doubles the damage of your lightning skills. Coupled with Undine's, you'll be seeing very high numbers
Fire/Elect, on the other hand, focuses more on DoT skills. You get access to 3: Scorching Earth, Pheonix Rising, and Tesla field
As a Soul Master, you lack the defensive skills of a witch, so HP is very important. But Weight is MUCH harder to come by than HP, so I would recommend a high sense build. Pure MA would be best, imo.
Jewelia: PrettyUglyFox, Illiterate Sheep, RainbowKitty