They're all different:
Reason/Fruity Loops are good for bangin out beats, Reason is way better imo but there's people who swear by FL. Just depends which suits your work flow.
Pro Tools is a sequencer, you can put VSTs in there and use it, but ideally if you're gonna make beats with software, Pro Tools isn't the best choice, use Reason or FL.
Acid is good if you f*ck with loops and wanna match tempos and sh*t, it's very good for that.
And for downloading Reason.... I don't have a link, but look into torrents, I'm sure it'll be on one of them sites. Download a program like UTorrent, then go to
www.torrentspy.com or
www.piratebay.org or something and find it.