I criticize apps a lot in my videos because in many cases they aren't needed, and with a bit of coding knowledge you can go without.
That being said, there are some apps that are not easily replaced, and that I constantly use when working on my clients stores.
Just the one I've used most for whatever reason. I'm happy with it.
Really basic but sometimes that's all you need.
When you don't need any advanced features.
The only one that works flawlessly with Shopify.
Sometimes a client needs to set up lots of custom pages and they need control over those pages themselves, without my help and without editing code.
The leading app for creating custom landing pages in Shopify. Easy drag-and-drop interface. It's the most expensive app though.
I've used Pagefly a lot more than Shogun. It's almost the same as Shogun, slightly cheaper.
Automation & Bulk Actions for Big Stores
When you need to edit hundreds of products.
Tags products based on rules you set using other product info. e.g. combination of tags, variant names, title, type etc...
Import and Export CSV but only the fields you actually need. Way better than the Shopify default.
This app is powerful. Scripts to automate back-end tasks without Shopify Plus.
Referral / Affiliate / Reward Programs
Get influencers to market your store to their followers. Rewards can be payments or discounts.
Has a marketplace that helps influencers and brands connect.
Solid, tried and tested referral app.
More for discounts and "recommend to a friend" type of rewards.
Compression and SEO
Not a Shopify app, just a great website for compressing images
Shopify app that compresses images, adds alt text, and renames image files automatically in bulk.
Get customers paying for a product weekly / monthly / quarterly.
Yep, this is the only one that I recommend.
Sometimes you just need to hire someone.
The leading company for small Shopify development tasks. They match you with a developer and you can get it done in less than a day.
This is what I use when I need help e.g. design work
Only for small, straightforward and repeatable tasks e.g. cutting out image backgrounds in photoshop
This is a whole topic - see my favourite themes.