Best related select / sub-list plugin?

Hello. Interested int he classic related select scenario.

Countries in one list.
Cities in a second list.
Both lists are on the same page and both are active.

I want to make them related - so that the Cities list only shows the
cities that are appropriate for the selected country. As user chooses
a new country, the list of cites is adjusted. Very clear scenario yes?

What is the best practice or best plugin for this right now in April
2007. One of the difficulties of Rails is that things move so fast,
its hard to know what is current and what is outdated.

I know of two plugins

Sub-List Form plugin

Related select forms plugin

Has anyone compared them, or others that I have not yet found? Which
is best?