My personal thoughts:
Mani- I have used Mani since the very first server I created went live. I have found that it is easy to use, to setup and to maintain. I did not use Mani because of the message I found under ES autoinstaller:
Now, I personally never had one single issue using ES or Mani on any server I had ever run, but considering I haven't run a gameserver in quite some time, I decided to give SM a shot.EventScripts is a prerequisite for some other Source addons. We recommend avoiding it unless one of your mods specifically requires it, as ES can cause server performance problems.
SM- Started using this once I created the new servers simply because of the ES issue outlined above. It is quite similar to Mani regarding the GUI, but tbh, I found Mani to have more options available to it at the get go.
SM has been a learning (or re-learning) experience, and I have found other plugins to replace some of what I had lost in Mani. SM has been stable as well, not a single issue that I could find with its functionality.
As I needed a bank script for a server, and Sourcemod didn't have any reliable ones listed in their plugin database, I bit the bullet and installed ES to grab up the BBank plugin.
Despite the message on the autoinstaller, I have not run across any performance issues since installing and running ES.
Now, on to the ES vs no ES part...
I would really like to hear what other people think about ES and the plugins available to it. NFO isn't the only place claiming ES is horrible, I have seen posts by people saying they are moving on to SM. What performance issues are people reporting?