I'm a ukulele player and I use it to accompany my singing. I both strum and finger pick and have all sizes fom soprano to baritone and they all have their place.

I know a number of people who use it for a melody and there is an instrumental technique for melody playing called campanella which takes advantage of the re-entrant tuning. The principle of campanella technique relies on playing succesive notes on different strings so the strings carry on ringing after they are plucked. There are sites that have tab and notation for folk tunes played in campanella style. They aren't all in the usual folk keys of G, D or A. If you want to play in folk keys, then go for a concert or tenor. A soprano doesn't have enough frets to reach top B, though if you use the alternative ADF#B tuning you can manage the D ==> B' range on a 12 fret soprano that covers most folk tunes.

If you want a ukulele that will not get lost in a session, consider a banjo ukulele.