We currently have a application written in V7. It is mainly used on the desktop, but some pages are used in smaller screens, down to mobiles. It also has function that can be embedded into other websites.
Given that V7 will be deprecated in the near future we are looking at upgrading to either v8 or v10.
My preference is to go directly to v10 as this will avoid a second upgrade in a couple of years time. But - V10 does not seem to be totally stable yet and it looks like it will be a much bigger job.
So my question is - what is the consensus on the forum - should we go straight to v10 or is it better to go to v8 first?
One of the biggest questions to consider: Do you need to support IE11? If yes, then you should probably choose Vaadin 8. Vaadin 10 does work with IE11, but the performance is not great thanks to the needed polyfills.
I think migration V7->V8 then V8->V10 costs more than V7->V10.
From V7->V8, you have to change all the databinding + Table.
From V8->V10, you have to change the layout+navigation.
V10 is less stable than V8. V10 is better for touch screen. V10 is easier to extend but you have less Vaadin add-on. Make “custom” pages is easier in V10 than in V8. You can check this webinar https://vaadin.com/forum/thread/17146013/webinar-what-s-new-in-vaadin-10
If V10 fits your needs then go straight to V10. (you will have to rewrite huge parts of your app in V8 or V10)
(or, if you can, wait for V11 and test V10 
).