We've done both TL and BB many times and as of Sept. we did DC. We love them both-and like others have said, they are completely different experiences.
For me, and my DD8, the Dolphin swim was amazing.

And well worth the extra $100 each (only $50 however by using AMEX special deal-I got $50 back on each of us). My DM and DSis didn't do the swim but also had a great day. In fact, they thanked me for having us do it!
All food and beverages are included. DD7 really liked being able to get all the frozen lemonades she wanted. The Coral Reef was awesome as were the Ray Pool (no swimming with them, but feeding them was really great).
We went on a Sunday in Sept. and we overhead that the park was just at capacity that day (a little over 1000 people) The low crowds were really cool. We also heard that mid-week, there were only about 400 a day. Next time I will pick a mid-week day.
As far as TL goes, it's our fav. Disney water park. And yes, how often can you say I Swam with Sharks. We took my adult DNiece there for the first time in Sept. and she really enjoyed the Shark Reef. She and I did it a few times in a row with only about a 5 min. wait. We took our time going through-in fact the next group of swimmers passed us by. As long as you don't turn around you can take your time. However, it doesn't compare with being able to dive down with the fishes like at DC. There their sharks are behind glass but you still get the effect of almost swimming with sharks.
For us, DC was a great experience and I hope to do it again in a few years. However, we do do TL and/or BB each trip (as long as the weather is good) and always have a wonderful time. DC is definitely a more relaxed feel-they are no rides, etc. just a great way to spend a day being with your family and ocean creatures.
If you can only do one or the other, and rides, etc. are more important than snorkeling, etc. then I would do TL. And yes, it is substantially more to do DC.
Have a great time either way you choose.
