For personal use I use Mind Node, primarily because of the ease of transition between the desktop and iPad/mobile apps.

For work I have been experimenting with Whimsical, Pletica and Coggle. Coggle is the closet to being a true Mind Mapping application, where as Whimsical and Pletica lend themselvs to more varied range of diagrams too.

Miro is a great tool that covers many uses.

Everyone on our team seemed to pick it up very quickly the first time we introduced it. It was great to be able to work on diagrams and files together live during interview calls with clients etc.

It also handles large files rather well. Sometimes we could have thousands of notes on a Miro board with 4 active users and it would still function, albeit a bit slower on older laptops — but it worked.

For personal use I much prefer Mind Node, however.

I like to start with outliner tools like OmniOutliner to get my most roughly-shaped thoughts out on the page (but even apps like Apple Notes will do in a pinch). Using a technique I learned from improv comedy, I start by writing one thing like "communication app", and then saying to myself "yes, and then what?". I keep repeating this process until I've filled up the page with thoughts (most of which end up being ridiculous, but the idea is just to get as much out on the page first and leave the judgment for later). Afterward, I try to solidify/crystallize these thoughts and tangents into something more meaningful: I'll usually do this in an app like iA Writer where I can remove all the distracting parts of the interface and focus on writing. Having the outline is super valuable because I can always refer back to it when I get stuck. I try to never change the outline once I've written it (only ever append things to it, never remove) because even the "useless" tangents might turn out to be useful later.

I haven't used it in a bit, but used to like using MindMeister for mind mapping and team brainstorming, as then you can turn the mindmap into a project in MeisterTask in a click.

And as @crabl mentioned, OmniOutliner is great for outlines and moving ideas around, even if not linked as in a mindmap.

For web-based clients:

If you're looking to collaboratively create a visual diagram that's mostly labeled and inter-linked shapes, Whimsical is my top pick.

If you're thinking about using a mind map as a way of writing and thinking, I'd recommend Plectica. It has a really nuanced interactions around nesting, linking, and filtering — while elegantly supporting LOTS of text and images.
Kinopio Club is building an experimental, super cute, and rapidly developing mind map tool, to "help you think through your hardest problems". It's really unique, relative to what's out there!

However! I generally prefer Mac apps. I find that web mindmapping clients tend to have performance and usability issues, and they're often evolving so rapidly that it makes my documents feel a bit unstable.

Like a few other folks in the thread, I really like MindNode for Mac and iOS. There have been several major versions in the past few years, which have gotten better-and-better over time.

Omnigraffle is the most advance Mac mind mapping tool, if you need more nuanced map design, but want to stay with a true-to-form Mac app.

My favorite mind map tool of all time is Scapple! It has a very barebones, almost dated (like something from 20 years ago?) aesthetic — which to me is perfect. With zero bells and whistles I find that it's the tool I've kept coming back to for mapping out thoughts, over the years.

I am using coggle due to minimal and fast. i don't like complexity. You can try.

Keynote on iPad
OmniGraffle