No, I haven't. I've primary managed projects over the years using various amounts of trac, basecamp, ms project and even mediawiki.
It's important to note, however, that it's not always about features, and my first impression of MantisBT looking at it now was mostly defined by usability, so much so that it's hard to tell what features it actually has.
The interface on the demo is very noisy. Redmine behaves like a modern web app, MantisBT appears to behave like a no-frills, late-90s bug tracker. That's probably fine for a certain set of developers, but I use Redmine because it's a replacement for both Basecamp and Trac (and fits the workflow of me and my company better than each), and I'm able to use it to manage non-technical projects with non-technical members alongside technical projects with technical members.
Usability is hugely important. It's not just an asthetic issue. Take, for instance, the issue listing:
Especially in the second example, I have no idea what I'm looking at. There is so much information that needs to be digested before I understand what's going on, and it's hard to digest it because there is a lot of visual noise and overpowering colors. And then once I figure out what's going on and decide I want to look at a ticket, I have no idea what I'm supposed to click to open a ticket (apparently the ID)
In contrast, here is Redmine's version of the issue listing (this isn't my project, just an example with the same theme):
Thank you; you pretty much echo all of my current frustrations with Mantis. :P
MantisBT appears to behave like a no-frills, late-90s bug tracker.
To be fair, Mantis was started in 2000, and the look and feel hasn't really changed since then, mainly because of no good separation between code and presentation; templates are one of the always-on-the-roadmap-but-never-implemented features simply due to having a very small developer team.
Also, I would argue that from a neutral standpoint, but bug listings have a similar level of information density. However, Redmine does a good job of hiding all the unused filters, and an even better job of not looking visually overwhelming. Part of that has been improved recently with the new colorscheme for bug statuses, but there's still a lot that could be done.
Well, the key feature it lacks for me is that of "not being written in PHP". That might not sound like much, but it means it can't fit into the rest of my Ruby infrastructure, so isn't even in the running really.
