Here’s where I place the stress in these words (’ for primary stress, “ for secondary stress, mark precedes the relevant syllable):
a ‘ris to “crat
“a ris ‘to cra cy
‘a ris to “cra tic
(Actually, the weight on the first and fourth syllables is just about even in aristocratic.)
I think this pattern for aristocracy is universal, right? There’s only one way to go with those -ocracy words.
For the other two, I am aware that other permutations are common but I don’t know whether these follow national/regional trends.
So, is one of these considered standard in England, the USA, elsewhere? How do _you_ say them?