Depending on how much work you want to do, I would say BIAB is easier to get up and running. It essentially generates an accompaniment for you based on the chords, tempo, and style you choose. Some say it is complex. It does have a lot of features in from the years of growth but most are not needed to get very good sounding accompaniment. With the addition of RealTracks and RealDrums, the sound is awesome.

RealBand does most of the same but gives you more control over your tracks. If you're used to Sonar or something, RealBand should give you no problem. I'm still a BIAB user at gigs. I am playing around with RealBand and it is on my list to move my BIAB songs into RealBand once RealBand matures a little more and works out the kinks.

My advice would be purchase the BIAB package that includes RealBand and spend a little time with both. This forum has a lot of experienced people who can help with just about anything.

Rachael