They both have flaws for sure, but I wouldn't go as far to say they suck. The list of things you can do with them have real benefits. Like hands free texting when driving.
The review videos show off plenty of things people can use them for, but not likely on a daily basis aside from asking the weather or setting timers and alarms.
There are some things I would like to see changed with S Voice. For starters I hate the blue bubble "Say your wake-up command to wake me up" always being there. I also believe S Voice should show scrollable windows when it shows results on Wolfram Alpha. That way we won't need to scroll up to see what we searched. I've seen a few different videos of people testing the humor side of the virtual assistants and I must say Siri wins in that department. But then again, the assistants are not meant to be a toy. (I still hope Samsung adds some more humor to it.)
I doubt a whole lot will change with S Voice before it launches elsewhere, but it is a for the most part unreleased product (Dubai has released the S III I believe) and like Siri, it is a beta product. We will see more updates and advances eventually.