It's very much a "How long is a piece of string" type of question and it really depends on your (business) requirements. EM 13.3 is the most recent version and has the benefit of having been released for the longest time (In terms of the EM13 product family)...so (In an ideal world) that would suggest greater stability.
The EM announcement dates don't necessarily tie in with OpenWorld and the release dates of any new version is classified information with snipers ready to take out any leakers ;-) It's also uncertain whether or not OEM will be following the annual release model, there hasn't been any news in that regard.
Hope this helps
Thanks Ian, it was pretty much what I was expecting - have you seen a recent, official roadmap document for OEM?
The closest I found was a slide or two in this presentation from last year:
Yes, there was a roadmap in the collab session, i'll see if i can find the download. Not able to find it on collab right now. The plan is annual release with an additional plugin update each year. Times will not be committed obviously.
If you're at 184.108.40.206, I would consider the upgrade to 13.3. It will be an easier upgrade from 13.3 to 13.4 later on. You'll want time to do testing, etc...