Just for basic general use : internet, photos, videos  At this level are  there any differences ?  Both are about 5000 baht. Or is it only at the advanced and complicated functions where there are differences ?

Note 9 is the better of the three.

25 minutes ago, chuang said:

Note 9 is the better of the three.

 

Perhaps. Perhaps not. Note 9 doesn't offer 4k video Note 8 does.

 

https://www.gsmarena.com/compare.php3?idPhone1=10192&idPhone2=9814&idPhone3=10171

 

OP might want to use the site above for comparison of any other devices under consideration.

4 hours ago, Farrows3399 said:

At this level are  there any differences ? 

I don't know about the other 2 but have recently purchased a Note 8. One negative is the weakness of the wi fi - have a look on the MI Community pages as no. of complaints. Very slow for me switching from one wi fi to another and often have to manually refresh even when getting home if I have used elsewhere.

 

Still on Android 9 with no date to move to 10.

 

Also a lot of Chinese bloatware and ads unless you are happy to take steps to remove.