I own a 5 string Bass, a 6 string fretted Bass, a 6 string fretless Bass, a 7 string Bass and two 4 string Upright Basses. I am infinitely most compfortable on my two 6 string basses and my 3/4 size upright bass and so I use those three instruments on almost all of my gigs. 5 and 6 string basses allow easier access to more range in less hand positions..... You can play more notes without moving your neck hand as much and they have a greater range than 4 string basses. In the music I play most (Jazz), I find my 6 string basses to be extremely useful and valuable and yes I do take a lot of solos.