Good luck floating on labor day. The river is going to be so congested with floaters, It kinda takes the relaxation out of tubing.
Frio is the most pristine and clear river for tubing. The scenery is breathtaking, but its a good 3 hour drive out west.
Guadalupe is not bad, more space than the san marcos and it isn't as cold. You gotta drink a lot of beer on the san marcos river to keep warm.
"The way to see by faith is to shut the eye of reason."