Speaking as someone who had my first ever solo gig at the KFFC folk club last November (I usually perform with my band, Elowen) the sheer terror and trepidation I experienced beforehand made me wish that the rest of the gang were with me...but the time spent gigging with my band, playing around with mics etc stood me in good stead, and I had such a blast that I'm now touting around for more solo gigs (and I've been invited back, so I think I did something right!). The joy of singing in a band and being able to harmonise (which is my big thing)is fairly incomparable as we are dedicated bunch who care about the sound we make (and with 3 and 4 part harmonies we need to be 'disciplined' - with a certain amount of control, but not freakery), but trying to get everyone available for a festival gig around organising our families can be awkward - so being able to fly solo is an advantage there!
if you can - do both!