I have been using imacros for 10 years and for 2 years ui vision and with a lot of study you can do the same automations with both.
Imacros is easier to use but has fewer commands.
For the very simple jobs I can do with an old firefox brower ESR 52 imacros use (works all day and requires little memory), for the most modern jobs I use Ui vision with firefox 81 (I use an updated browser for security and I can automate modern sites as well).
Ui vision disadvantages:
Slow (I set speed fast and timeout 1 seconds)
Code macro more complex (need multiple line)
No relative position (xpath)
For some command require xmodules (need installed in machine)
Free user limited xclick/xtype
Sometimes not work for random bug (IPC or kantu is not connect to browser tab)
Work in old firefox only
Have not image recognition
Have not a solution to counts csv line (you must know the loop number)
Have not IF/ELSE/REPEAT
Can not automate addons, bar menu, internal browser page
Have not desktop automation
Some sites cannot be automated with imacros as they are incompatible with firefox 56 and you have to visit them with updated browsers, for example github requires a modern browser so using ui vision is mandatory if you want to automate everything today.