The most common size!
Normaly tuned the traditional way in a-d-f sharp-h (called d-tuning). Today's more favored tuning for the sopran is the c-tuning g-c-e-a.
The Concert Ukulele is a kind of "in-between size". There are no standards set for it. Its scale is normaly made somewere between a sopran and a tenor size. Especially for grown-ups and people with "bigger" fingers prefering to play the whole fretboard, it might be the perfect size to think about. The standard tuning for a Concert Uke is normaly similar to the Sopran: g-c-e-a.
The next bigger size is the Tenor Ukulele pretty loved by soloists. Tuned the traditional way (a-tuning) it would be done in e-a-f sharp-c sharp. But nowadays it has become naturalized to tune the Tenor Uke in g-c-e-a (like a sopran ). BUT ! mostly then with a lower g which will expand the tone range.
The Bariton Uke is the biggest and the deepest in tone. Its tuning is exactely the one of the higher 4 strings of a regular guitar : d-g-h-e
This way a guitar player might feel very comfortable to learn the Uke pretty fast coming from the guitar. Here counts the mini/maxi rule: A minimum of instrument produces a maximum of tone. The Baritone Uke is perfect addition to an Ukulele ensemble.