I really like pivotal tracker, I'm using Asana right now for my personal project.
I'd go with whatever's easy. Issue tracking which is too rigid ends up being a burden
I used Jira a long time ago, but now we are currently using Restyaboard which is far better than Jira. It is flexible and has more free features to use. A better alternative to Jira.
Avoid Zoho, it's slow as shit. Typing up ticket the text latency is nearly a second.
Kinda liked Assembla - doesn't look great and search isn't great, but it's simple and quick enough for most part.
I've really enjoyed using clubhouse [1].
Height[0] is also similar to Linear.
Trello? I think it is owned by atlassian FWIW, it’s good for smaller projects
Compared to more modern tools Jira is actually not very flexible.
For me the most flexible and useful tools are Kanbanize[0] and Kaiten[1].
Both companies are engaged in furthering the Kanban method which also means they care about having a lot of features for displaying cards, limiting work in progress, defining workflows and have solutions for working together on bigger workflows with several teams.
I use both professionally.
A lot of other solutions have assumptions built in which really limit flexibility. One example in Jira is the coupling between workflow status and columns on boards.
[0] https://kanbanize.com
[1] https://kaiten.io