In order of preference & cost. The cost is a rough ballpark price.

1. Cordoba 15-CM   $70-100   *This is what we use in class.
2. Kala 15-S     $50-80
3. Fender Concert or Soprano    $100-130
4. Makala Dolphin     $40-50 Soprano
5. Ohana CK-10     $50-80

I personally prefer Cordoba or Kala brands. I own both.

You might want to also consider a bundle which would include Ukulele, a bag/case, strap, and tuner. Some also may come with extra strings and/or a basic song book and chord chart.

Amazon top rated bundles:

Lohanu (LU-C) Concert

https://www.amazon.com/gp/product/B015XD4YLY/ref=as_at?imprToken=8Hvlatd77Efa-f8f5hk4qQ&slotNum=4&ie=UTF8&linkCode=sl1&tag=cmuse4425-20&linkId=15e21d8c60081a4abddd09fee08519dd

Kala MK-S Makala Soprano bundle:

https://www.amazon.com/Kala-Soprano-Ukulele-Instructional-Polishing/dp/B005ETZEJO/ref=sr_1_8?s=musical-instruments&ie=UTF8&qid=1536516211&sr=1-8&keywords=ukulele+bundle

Great general Uke information such as sizes, types, and brands:

https://www.cmuse.org/best-ukulele/

https://www.guitarfella.com/best-ukulele/

http://www.voicesinc.org/best-ukulele-for-advanced-players/