1. Tablature Scroll vs Note Highway. IMO the RS note highway is clunky and difficult to read (especially with fast runs) and it significantly reduces the amount of fun I have playing the cover songs. Maybe its becasue I've spent years looking at tablature but for me, the presentation of the BF tab scroll is a million times easier to follow. The tab scroll also indicates timing in a far easier to understand format. So on this basis alone, BF is my preferred choice for playing the cover tunes.
2. Recording. The fact that BF records almost everything you play and then gives you the option to save the recordings is absolutely key for me. I've played in bands for years and without a doubt, the single best learning tool for the bands as a whole has been to record all of our rehearsals/gigs. Its easy to think you're nailing something while you're playing it. There are times when I've finished playing a song and thought I totally killed it. And then I listened to the recording. Yikes! Recordings don't lie and have been instrumental to my growth as a player. Not only that but being able to quickly record riff ideas is also great. How many of us have come up with awesome riffs when just screwing around and then think we'll remember it later only to totally forget the idea? So the fact that BF records everything and also allows for recording over a blank backing track is reason enough for me to buy the game.
3. Videos. I'm a fan of the music videos that accompany the BF tab scrolls for for several reasons. First, I just like the videos. Most of them I've seen before but a few I haven't. Regardless, I like having them, especially when playing songs I know fairly well. Also, it makes it more intetresting for anyone else in the house to watch when I'm playing. Just looking at a tab scroll or a note highway can be pretty boring for on-lookers so the videos add something else to watch. I also enjoy the videos from the professional players. As a bass player I would have preferred if they included a few more bass players besides Bootsy but I still enjoy the videos from guitar players.
4. Ducking. This is a no-brainer in terms of its usefullness. Being able to remove the bass tracks from tunes is incredibly important in terms of learning to properly play a cover tune. If the bass line is present, its easy to sort of fudge your way through the song because your ears hear the right notes whether you are playing them or not. Its one of the key reasons why guys who have never played in a real band before sometimes struggle when they play with live musicians....even if they know the song perfectly when playing to a recording. Playing along to a bass track is a sort of crutch and its easy to think you really know a song when in fact, you might not. Recording also comes in to play here as its incredibly helpful to record and listen back to exactly what you've played with no bass line in the background to fool you into thinking you've nailed something you haven't. Lastly, ducking allows you to also think and play outside the box if you want. Maybe you have a different idea for how something should be played. With no bass track to follow, you are free to explore whatever and whenever you want. If the bass track was present, it would sound like crap and get all muddy if you veered off the path but with ducking, you are free to play whatever you want. And record it! I can't overstate how important this is to me.
5. Song Selection. This is highly subjective but I prefer the songs as a whole in BF moreso than RS. I know RS has more songs available (and some overlap exists between the games) but I find that I enjoy playing almost all of the songs in BF and probably less than half in RS. But as I said, thats totally subjective.
6. Vocals. Allowing for vocals not only makes the game more versitle and interesting, it allows for a more social game experience. My wife doesn't play guitar or bass but she can sing so we can jam together. Also, I'm a lousy singer but after working with the vocals a bit, I've shown (admitedely small) improvement.