First off, this is too far ahead of time to be 100% certain of flight schedules.
But I will say that you have painted yourself a bit into a corner here, given what the
schedules say now.
The evening flight on Sunday is the cheapest option by far, but carries a bit of risk that
if it's delayed or cancelled, you may not make it to Athens before the start of your
trip on Monday.
If you want to consider traveling on Saturday to give yourself a bit of a cushion, there
are not very many options in the daytime and the connection in many cases is pretty
long, and many of the flights are pretty expensive at this point (I don't know when your
tour ends on Saturday and thus when you could get to the airport). Ryanair has a nonstop
at 10:05am to Athens on Saturday, which you probably missed since Ryanair is not
always listed in online 3rd party searches.
I don't think your concern should be Aegean Air; it's a member of Star Alliance and is
a reputable airline. And for the most part, who posts a positive review these days (i.e.,
most of the reviews you're going to see are negative ones). You actually have a smaller
window of time and fewer options than you may think.