Which is better, frostwire or bittorrent?

Neither. Avoid p2p software like Ares, Limewire, Frostwire, Bearshare, torrents etc. -* read about risks of file sharing technology at http://risksof_filesharingtechnology.blogspot.com

If you want to safely download some free music, http://searchformusic.eu.pn/ searches many safe, no-registration sites.

Also, don't use (YouTube) video converters (low quality music & sometimes adware from the converter).

Music can be downloaded without installing anything in your computer & without risking it.

Bittorrent