The clip-on tuners are great and I use them extensively ... but not at gigs! They disappear way too easily ("disappear" as in go walkies and never come back) and they look ugly as sin.
My Korg DTR2000 on the other hand looks really cool, and with a fly lead left dangling from it, can also be used by the guitarists in the band.
Where space is short, or there's no need for me to bring that particular rack case, I always use a pedal tuner. First choice is the Pitchblack, but increasingly the only pedal I take to gigs is my Valetone Dapper.