Both of them are some-what equal but I like Speedbit Video accelerator.
How they work:
Speedbit Video accelerator supports all the websites and all browers.
See supported sites:
SpeedBit Video Accelerator - Supported Video Sites
You can also download videos with speedbit video downloader.
The best part of it is that even if you are downloading a file using a downloader like DAP or Flashget , it will accelerate that download also. You can also use proxy in it. One more thing, it takes very less memory than the other softwares. And you can able to see the difference by using it , So, just give it a try.........
Click here to download.
I download 3.5 GB+/ day and total 100+ GB / month