Also Autodesk Graphic. It's by far the best iOS vector drawing app, despite being a bit buggy in places. Combined with iCloud I can start an illustration on my iPhone, continue on the iPad and then finish off on the Mac.

Shameless plug – this is an ongoing collection of vector doodles I've made using Graphic on the iPhone: https://www.instagram.com/shapeslinescolours/

I haven't used the iOS version, but you should check out Affinity Designer. The Mac version is amazing (better than Illustrator IMO) and I'd have high expectations on iOS. The Mac version is well worth the $50 license.

yes please. Especially for image tracing, coupled with the ability to take photos straight from the device. PLEASE!