Actually, i find its the other way around, i have been playing on prince ever since i got the game and was only able to win *once*(out of about 15 tries, although im sure i couldve won some of the games if i had tried harder but i usually quit when it starts looking bad).Agressive AI should be the standard setting in my opinion it makes games so much more realistic.Actually about difficulty i find that Noble with Aggressive AI is harder than Prince without aggressive AI.
In my last game with AGG AI on I was really astonished noticing how much AI has improved, Justinian desembarked around 50-60 troops on 3 different landing sites, fortunately i was more advanced than him so i kicked him ass without no problem but in a different game these landings could have been really deadly.The only negative point is that AI now uses planes to bombard but doesn't use them effectively in support of an invasion.
IMO if you should choose between scaling down of a level with Aggressive AI on or playing at an higher level of difficulty, from a gameplay perspective it's really better the first case to enjoy civ4 because warfare and nation building are both present, and AIs seems just smarter.
Today after reading this thread i thought id try aggressive AI and decided to set it to noble instead of prince and managed to win the very first game i played. Played it on a big & small as justinian(picked random) and didnt have access to iron until i had conquered my neighbour.
In short, it was a hell of a lot harder(or should i say time consuming) than usual to conquer stuff but it didnt really matter as all i had to do was bring enough trebs and at the end of the wars i found that i hadnt lagged behind in tech as much as i usually do during war time.
It may just be that my playstyle is better suited for playing against aggressive AI(i find it too annoying to manage large empires which usually means that by the end of the game at least one AI has managed to grow ridiculously large and eliminated any chance i had of winning) because i just conquered and vassalized everyone without risking the AI getting a tech lead.
I think ill keep playing on default AI as i actually found it more challenging
