Hey! Not sure if any of you working in an agency are facing something similar to this? An e-comm client of ours has signed of a large website upgrade (from Umbraco 8 to the latest version) and are on a tight timeline. We think the best thing to do, would be to build in 14, because the difference between 13 and 14 is quite significant and if we build with 13, we will have to rewrite a lot of the custom backend, when we want to upgrade them to 14, which will be a couple weeks of work minimum and they will not be willing to pay, after having just paid for a large upgrade. However, 14 release is not yet completed and there are still some large elements e.g. the grid missing. We arent sure whether to just progress with 14 and hope for the best. Is anyone facing something similar? Does anyone have any thoughts?

I would use 13 it is a LTS so has a longer EOL than 14

yes but inevitably we will have to upgrade to 14+ at some point and 14 is significantly different to prior versions.

I would also suggest 13 for now, because it is more stable at the moment then 14. Also a lot more packages are available (at this moment) for 13, not yet for 14. And with 13 you can still go on for a couple of years, before an upgrade (perhaps to the next LTS, which is 17) is needed.

I also agree, go with v13 as it is LTS and for a paying client. You could build your backend custom UI in v13 using the UUI https://uui.umbraco.com/ so there is less to change when you upgrade to the next LTS which uses the new backoffice.

Agreed v14 is definately not ready for implementing a client solution.