I've been building support and dev/ops ticketing systems for years and I still haven't found a platform that suits all needs.

For my latest startup I went looking for a service desk tool. The key criteria was "feels like email". The moment any alternative required a user signup just to lodge a support request, I ruled it out.

I ended up choosing Groove. I don't recommended it. All ticketing systems suck, this one just sucked the least for my support desk. Groove doesn't extend to other ticket types, and it's nowhere near as flexible or extensible as JIRA, and the mobile experience is horrible. But it does "feels like email" for my customers better than every alternative you care to mention.