Ignition Hands down. Not just because of it being a full blown SCADA, but because the documentation is well ahead of other offerings and them providing free training for that platform.
Yes, learn it using their documentation which excellent.
Stay away from their YouTube channel; I spent weeks cursing them and down thumbing their videos, substandard garbage. They assume knowledge that you will not have for sometime andhhave no logical, practical or sort os sequenc.
That applies also to some of the video tutorials they have on their websites, outdated or suddenly jump/skip topics.