I wouldn't hesitate to tube down the Hudson north of, say, Orange County.
My extended family went to NB and stayed on the Comal for years and years. I grew out of it about 15 years ago, probably closer to 20 to be honest with you. It was once a quiet little river and now it's a fucking carnival sideshow. Fuck that, I wouldn't go near that shitstream if you paid me.
On the other hand, I have fairly recently tubed the Frio and enjoyed that quite a bit. Of course, there's no water in that particular river at the moment.