I’ve used OmniFocus but I feel like it’s just too huge and involved for my needs, but I won’t 100% rule it out now. 
What I think I want is an app/system that’s primarily to be used on iOS
What would you recommend? Thanks!
I use Remember The Milk (Pro):
Essentially RTM is just a set of lists of tasks (and thus less complex than OmniFocus).
I have long gone back and forth on trying to find something that works for what I call TERN (Tasks, Email, Reminders, and Notes). Because I run Windows 99% of the time and I own an iPhone, I’m at a frustrating cross roads when it comes to native apps that can be on both my Windows machine and work decently enough on my iPhone. So, almost immediately OmniFocus is out. Beautiful app, tried it, liked it, but don’t want to be on my phone for everything related to it.
Remember the Milk, I know it sounds petty, but I really don’t like the name or the design. So, that’s out.
I’ve been through countless others and have cast them all aside for one reason or another. I’ve been down the Evernote and OneNote roads (OneNote kind of hangs around at the moment, but it’s not responsible for task management; just doesn’t do well.)
There is Microsoft’s acqusition of Wunderlist that they made into “To-Do”. That one is decent enough because it does synchronize with Outlook, iPhone app, and Windows 10 app. Not quite sure why I don’t use it. I can’t put my finger on it.
TL;DR, currently for TERN…
I would like to mention I rather like the update Google has made recently to their interface and they finally updated their task system. I think they just need a few more features to draw more people to it.
Oh wow, that’s a blast from the past, I didn’t even realize it was still around.
Wow, we’ve been through a lot of the same thought processes, thanks.
The struggle is real.
Things 3 for my personal stuff, GLIP from Ringcentral for shared tasks and projects.
Just something to consider is one or more plain text files on a cloud service and using the TaskPaper format. I like to use Editorial to edit my TaskPaper files on iOS, but I can access them from any platform (including web), and automations involving text files are probably the widest of anything imaginable.
To put my own circumstances in context, I use TaskPaper for a lot of my transient to do lists. I use Asana for projects where shared responsibility and viewing is beneficial (but many other platforms have better integration in my opinion)… and ToDoist for my shopping list as it integrates with Amazon echo for adding stuff to it.
ToDoist is multi platform, has great integration options; but probably comparable to some of the other suggestions. Plain text files though are something with so much potential if automation happens to be the *key* aspect.
Used Toodledo for many years…very flexible, cross platform, shareable, etc.
I’ve tried almost all of the apps over the years but keep returning to this one.
Liking for the pettiness re Remember the Milk name & design 
I liked Omnifocus but for my needs I had the same thoughts as you. I switched to Todoist and am very happy with it. It has enough power to handle my needs but not overly comples.
For now I’ve settled on OmniFocus but I don’t like the fact that you have to open an item to get to the note and it can only have one note with it. Tried Agenda but don’t like it for reasons I couldn’t explain. Still looking.
I think Todoist is one of the strongest task management platforms for automators. It is not as feature rich as omnifocus, but the fact that it is based off of an API makes it so powerful for cross platform users such as myself. I have an android phone, an iPad Pro (main school device), and a windows PC (main creative/professional), so I am all across the map. Todoist works with all of them, and supports automation on all the big platforms, Zapier, IFTTT, Siri Shortcuts, as well as the major voice assistants* Google Assistant, Siri, and Alexa. Todoist also allows projects to be exported and imported as CSV files which opens up a whole different world of automation way to deep for me at this time. This flexibility makes it the best tool for me.
*Alexa and Google Assistant integrations work, but barely. They are clunky and unusable thanks to the way Alexa and GAssist handle 3rd party apps, but it shows that they are at least trying, and that it can work.