I've done a dolphin swin in Israel as well as DC. Israel was cheaper, but didn't have as many other activities to do. The dolphin swim in Israel was longer, but any "interaction" was completely at the dolphins discretion, my ex's group had a good swim with a mother bringing her baby into the group to say hi (apparantly the first time this had happened) and they stayed for maybe 15-20 minutes, my group didn't have such a good swim as the dolphins were busy with each other and all we saw was them swimming past at great speed, in a less controlled environment that's the risk you take. For some people this may be their prefered way of doing it, but if you're on limited time and want to make sure you do get some interaction with the dolphins, the DC method is a safer bet. In my experience it is unusual for you to get more than 5 or 10 minutes "playing" with the dolphins no matter how long your "swim" is scheduled for. They tend to get bored with people after a while and go play with their own kind.