It's so .. Ukulele Underground of this place to reply to a question asking "Entry to Mid Level Soprano or Concert Uke Suitable for the Blues" by suggesting a Martin.
All the original blues musicians played what was available or made it themselves. Many (most) of these instruments would be considered unplayable by the standards of this forum. There was no education, no Youtube, no boring Youtube reviews.
My advice to you, OP, is to get a cheap uke and make it sound good. And when you can do that, you can decide which one sounds good for the music you want. These things are totally subjective. Personally, I like a really cheap baritone uke for blues. Or a soprano.