I know FlowRouter is the popular choice, probably because it is specifically mentioned in the docs, but I do hope more people (especially those that are new in Meteor, in 2020 btw) consider using Iron Router and Blaze in their new projects as well.
I myself am just returning to Meteor after I first heard it, and back then I was still a junior dev, so I mostly opted to use easy to understand tools for development because I was the only web developer at that time from where I was working (looked for mentors, found none, thank the heavens for internet).
I spent way more time reading docs of various routers in Meteor (analysis paralysis sucks), and I seriously thought Iron Router has the best documentation. It’s both clear and shows code samples that are easy to understand.
And it supports what I’m looking for now, a way to have client routes and server side routes (I need to have REST endpoints for external applications).
Before, I was constantly looking at the “next shiny thing”. I tried React, didn’t work for me, I’m not as smart as most people who uses it, and certainly not advanced (maybe after 2yrs, after I finish YDKJS) in JS enough to make efficient use of it. Later on I found Vue and was extremely happy with it. Then I got a good combo using NuxtJs and AdonisJs.
But when I heard Meteor got a new family in Tiny, I went back and took another look, and am now deciding to stay for as long as I can.
I am now (hopefully lol) not easily swayed by FUD (Fear, Uncertainty, Doubt) posts, most of them are because it’s easy to fall into architecture pitfalls anyway (which can be solved by refactoring your code using best practices, which Blaze has in here).
PS: One of the main reasons I took another look at Meteor also was this post.