I'd agree Ultima is nasty tasting (I have the same reaction to anything sweetened with stevia).

Of course there are other options. From your choices I'd say you are looking for electrolytes without calories/sugar based sweeteners? I personally use NUUN and I love it - its a tablet, but you dissolve it in water to make a drink. Others here use Elete - it is tasteless - drops you can add it to any drink of your choice (or plain water for that matter). I think Luna may be making an electrolyte replacement now too.