Haven't heard of this tool until now. Say I already use wget (or curl) for command line downloads. Besides the ability to download torrents, why should I switch?
The biggest feature is probably being able to download a file from multiple URLs (or with multiple connections, if the server imposes a per-connection speed limit) at the same time
I for one prefer aria2c's ability to download a huge file via multiple parallel streams using the -x switch. AFAIK wget doesn't have this feature.