I've done the tubing and it was great. I haven't doen the rafting, so I can't make the comparison for you. I will describe the tubing, if that'll help.
The tubes are large inner tubes with bottoms in them - so if you float too shallow you won't scrape your own "bottom" - I really liked that part!
There were several small rapids in the river and it was exciting enough for me being in a tube without any paddle. I've done rafting at other locations and love the excitement of the big rapids, but I wouldn't want to do that without a paddle!
Most of the time, we just floated - it was quite peaceful and calm. The area was shaded well, so it wasn't too hot. The guide pointed out local flora and fauna on our way. We got out of the river about half-way through to get a drink (extra money here) and see some of the flora up close.
We really enjoyed ourselves - it was just the three of us in our group.
Always a new adventure, always a new friend to meet!
Fantasy to Bahamas - August 2000
Fascination to Western Caribbean - May 2001
Enchantment of the Seas to Western Caribbean - December 2002
Voyager of the Seas to Canada - June 2004
Sensation to Western Caribbean - December 2004
Victory to Western Caribbean - May 2005
Zenith to Bermuda - July 2006
Destiny to Southern Caribbean - May 2007
Liberty to Western Caribbean - May 2008
Golden Princess to Alaska - June 2009
Next cruise = way overdue!