Upgrade From Version 2.1.3 To Version 3.1 or 4

- Yes, I will go for option 2, for many reasons: 

• CodeIgniter 3.1.11 work great with the latest PHP & MySQL version, 
  
• CodeIgniter 3.1.11 is very stable,
  
• Less work for the upgrade
  

- CodeIgniter 2, does not support the latest PHP version,  I think does not support PHP 7.x and up

- CodeIgniter 4, you need to rewrite lot of thing, maybe everything

Thanks Halim and agreed Option 2 is the most cost effective and faster approach as we don't have to rewrite the whole application due to the major changes in CodeIgniter 4 framework. The only thing not clear is do I have to go through multiple upgrade steps (e.g. From 2.1.3 to 2.1.4, next 2.1.4 to 2.2.x and then 2.2.x to 3.x.x) or I can directly upgrade from 2.1.3 to 3.x.x.

Thanks,
SauGo