Looking at the Adafruit page, it looks like it is has one or two things the TLC5940 from Sparkfun does not have:
- It's an i2c-controlled PWM driver with a built in clock, evidently in the TLC5940 family, you need to continuously send it signal tying up your microcontroller, while the Adafruit, operates independently once given the commands.
- 6 address select pins so you can wire up to 62 of these on a single i2c bus, a total of 992 outputs
- Terminal block for power input so that you can wire up the servos from this power source -- from the picture, it looks like Sparkfun may have this also, as there are two holes in the top of the board, but it isn't called out
I haven't used either of the two boards you asked about. While both seem to be competent companies, I tend to go to Adafruit frist, and then look to Sparkfun if Adafruit doesn't have what I want.
You might also look at pololu.com, which has its own controllers for robots. Here is their Mini Maestro 24 controller: http://www.pololu.com/catalog/product/1356
. They also make versions with 6, 12, and 18 controllers.