We looked into the crocodile farm thing and apparently the animals aren't kept in very good conditions- this always puts me off going to animal places because it makes me sad...
The floating market is meant to be really good though, we didn't make it the last time we went but heard really good things from other travellers!
I've been to both, and would recommend neither, especially if the visits are organized by a travel agent because you'll arrive at the market too late to get a good impression of it (if that's even possible now).
For floating markets, try Amphawa and do it on your own. It's very easy and it's a lovely little town. Lots of places to stay along the canal, and the floating market happens at night. If you want to go to Damnoen Saduak , it's quite close and you can check it out very early in the morning before the convoy of tourist buses start to arrive.
Here's a short review of Damnoen Saduak by CNN International. I don't usually put much stock in reviews by media organizations like this, but I'm afraid that they are spot-on this time in including Damnoen Saduak in the list of the biggest tourist traps in the world ... http://www.cnngo.com/explorations/life/15-worlds-worst-tourist-traps-077541
If you go, try to get there very early in the morning.
As for the crocodile farm ... there are better things to do in Bangkok. The one I went to had snake milking (where they extracted venom from the fangs of cobras) which was interesting, but otherwise it was as uplifting as a troupe of (tortured) performing bears in a traveling Indian circus.