YouTrack is pretty great. So is TeamCity and they integrate well. The JetBrains instance is open so you can just sign up for an account there and play with it. Also you can run them both on-prem and they're pretty easy to admin if you do.

Space I haven't used. It seems like an attempt to reinvent both products in a GitLab style product which is a pity because the JetBrains tools are very mature and I don't think they needed a new product.

A decade ago when we used JIRA team-wide and not org-wide, some teams internally preferred YouTrack so they used that (until the whole org moved to JIRA). What bothered me personally was that fields were basically "unschema'd" and everything suggested every value -- everything was effectively a label field -- including typos, which are more common in a company where English is second language.

But that was a decade ago, and it could've been a misconfiguration on that team's part. It was also back when JIRA was more of a structured database with real issue types and not stories atop stories for all eternity.