I would have to say the worse of the two. One's a spell effect and even though it replicates a weather condition, it doesn't seem right to single out the spell (sleet storm) just because there's an alternate table entry.
However, the DC will be 10 + 3 (sleet storm) + caster's ability modifier + level of the spell you're trying to cast. Footnote #1 is often overlooked. If you choose the other option, it would be DC 5 + level of the spell you're trying to cast.