We have no spelling program at all in our district right now,
but teachers have chosen to use both of these as something to
help their kids teach spelling. There are advantages to both.
I like RSitton because it's ready to go, ready to teach with
your kids. With "words their way" there are fantastic,
research based spelling activities, but there is a TON of
prep work. WTW is also meant to have kids working at their
instructional level, as opposed to one size fits all spelling
list.
If I had to pick, I'd go with RS, just because it's easier to
implement, but both are good program.s