Legendary Tiki- neutral stats or -spd+res?

Honestly, if you're that concerned you might as well keep the other copy. You're sounding like you want to fodder one or something, which isn't a bad idea at all.
I would personally go for neutral. 35 Speed is pretty good for an armored dragon and can go even higher with Hone Dragons/Armors.

Either one is great, since her speed is enough to mitigate a good number of doubles, though it isn't enough to double much. And if you're planning on using Vengeful Fighter / Quick Riposte / Bold Fighter, her speed is not needed to be able to double on either turn.

She could also use the extra resistance in blocking out mages, especially the blue mage community. (I lean towards +Res / -Spd a little)

Do consider buffs also, as her great stat spread can be pushed even further. If her speed's kept at neutral, you can actually, maybe make doubles, or mitigate a greater number of doubles. Though she can still feel the damage coursing from armored doubling abilities.

She is an outperforming unit, regardless of IV's, and it solely depends on how you are willing to use her.

I would normally go with the neutral, but in this case I would use the -SPD/+RES one, with Bold Fighter and the S. Seal Quick Reposte 3. That way you don't have to worry about makeing follow ups and you increase her bulk which is great for her.