I have used a sneak boat a couple of times, but I have never used any of the other watercraft that you mentioned. So take this with a grain of salt.
If you plan on using decoys out in open water then I would go with a larger pontoon or kayak. Something with enough of a storage/cargo area for you to put a decoy bag. I have also seen a couple of blinds/grass skirts that you can drape on a kayak or pontoon and turn it into a floating blind. However, if you plan on sitting on the bank and using the craft to deploy decoys, not using decoys at all, or retrieve down birds, then the float tube would be pretty handy.