Whenever I change plugs on Rios, I use NGKs, part# 2382. They are just a standard resistor plug, which is what all those Rios came with from the factory. I believe they cost around $2 each, maybe even less.
There are platinum and iridium plugs available, but you could change the standard plugs multiple times for the same price. Platinum and iridium plugs will last longer, and possibly provide a very slight performance increase(noticeable???), but cost more. If you decide to go with these, I'd go with NGKs, or Densos if available. I'd stay away from Autolites, as I have seen them break off ground electrodes and cause engine damage.