ideal difficulty for using alexander?

[Senshi]

Difficulty usually is recommended to be used VH/M (Campaign/Battle, thats the usual way of display)
If you use alexander or BI or standard Rome doesn't matter that much, there are only minor differences, e.g. in BI or alex the AI learned to perform naval invasions and such...

I play with BI.exe and personally made the experience with several campaigns that the AI shows the most reasonable diplomacy on "Hard" campaign difficulty. On VH they all seem to have gone berzerk and attack everyone everywhere, no matter if they are far inferior in strength, on Hard I experienced many long-lasting alliances even with a long shared border.

[Aper]

Hard campaign, Medium (Hard if you are a Leonidas-wannabe) battle are definitevely the better settings using whatever .exe

When you try VH campaign AI you begin to think Gaesatae are reasonable and civil people...