Aquanaut,
Alexander and Silver Glen are much prettier and have a lot of fish. DeLeon's sole advantage (besides being closer to my house) is depth. Can't get any deeper than 25' or so at the first two (even inside the caverns), but can get 50'+ at Deleon (cave entrance at 25'). They are only about 45 minutes apart, and so are not mutually exclusive. However, if choosing, Alexander is the best of the three (was there on Sunday - there is a nice swim-through that is scary the first time doing it).
Silver River is beautiful, but, as mentioned, you will need a boat. There are, however, many gators and snakes along the way (I've been on the river numerous times and I would not snorkel it, at least not for any distance - there are some good swimming spots though). A better river for snorkeling is Rainbow River. A boat is better to have, but not required (but you will need a ride back to your point-of-entry, or a boat ride up the river). Note that no disposable items of any kind are allowed at Rainbow (food/drinks need to be in tupperware or the like).
As there are more springs than you will have time for, I recommend choosing what is most important to you (i.e., depth, beauty, caverns/caves, remoteness, manatees, fish, etc.) and prioritize along those lines.
Aaron has my cell (and we have already talked about a few springs), so please feel free to call me with any other questions or about maybe hooking up.
Thanks,
Scott
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