Wayne,
I'd stick to the Sac for now, more services should you need them and it’s a bit more navigable, if you choose the Sac be sure that you do NOT cut the entry into the Sac where it meets the big water at Rio Vista. Be sure you take it very wide and enter the channel closer to the north side than the south. There is a very large sand bar on the south side and I know someone that ended up in 2' of water and stuck there for some time, he had a real bad day!
Steamboat is very pretty but has no services other than gas at Snug Harbor. I'd advise the Sac until you have full faith in your boat.
I hope you have a safe trip and enjoy the Jazz Fest!