I have experimented with a pick on the baritone only sporadically. Playing the low tuned baritone ukulele among several high-G tuned ukuleles can make the bari sound a bit muted. A pick may bring a bit more pop in these conditions. I have also been a fan/reader of flatpick guitar magazine which is all about picking even though I try a pick only rarely. I try the tunes fingerstyle.
Below is a link to the pick advice of a premier ukulele enthusiast, Alistair Wood, from a recent post on Ukulele Hunt.