I've been using the BusySync 2.0 beta for some time now and find it very well put together. I reviewed it here. The Google Sync is seamless and I haven't had any errors. This application has entirely replaced Spanning Sync for me.
I'm told the official 2.0 release date is toward the end of this month so if you are thinking about making the jump, try the beta now. If you are sold, buy it before the 2.0 final release and you can get the old price of $19.95. It is going up to $24.95 when the new version comes out.