Second hand answer, based more on what I’ve heard than what I’ve read. Agreed with Dimitra Triantafyllidou in general, but it’d be good to hear from more classicists.
Homer is extremely far away from Attic in time and (to some extent) dialect. So in terms of vocabulary and grammar, it might as well be Phrygian if all you know is Attic. OTOH, if you know the vocabulary and grammar, I’m told that the syntax is child’s play.
The furthest away linguistically is Aeolic, and people don’t often bother to learn the dialect differences because Aeolic is so obscure. I did, so I actually find Aeolic easier than Epic.
Like Dimitra said, Xenophon has the reputation of being the easiest classical author, and Thucydides the hardest. I spend more time reading Byzantine learnèd texts, and unfortunately for me many of them chose to emulate Thucydides.
In the New Testament, Mark and John are very simple and modern linguistically. Paul OTOH is more learnèd, and can be convoluted. Then again, I have trouble understanding Paul in English as well.
Of the Byzantines, special mention goes out to the poetry of Theodore Metochites. It’s pretend Homeric, but he exaggerates all the Homeric idiosyncrasies he can: there’s not an <ο> he won’t try to spell as <ου>. I’m glad Michael Featherstone has made a career of translating his poems, coz I ain’t volunteering.