This one lacks many of the secondary features of other download managers like JDownloader, but it's ligther (e.g., JDownloader is written in Java so it consumes much more memory resources), it does what it's supposed to, and it's more efficient in terms of download speed. So it's my first choice.

For me, USD comes in at 2nd place to FreeRapid Downloader. USD works fine, but it just takes more time to download from a link than FRD. It also lacks the automatic checker that FRD efficiently employs. And the FRD interface feels much better.