Austrian airline vs. Air Lingus?

First off, looking at buying tickets now for next October is consigning you to months
of fare re-checking or potential buyers remorse because you're wondering if the
fare went down. You are better off starting to monitor fares and waiting to buy.
It may turn out that Austrian is cheaper than EI at some point.

Other than that, 1) customer service is partially a function of you knowing your rights in
case of IRROPS 2) I see it as a function of your constraints.

If you are constrained by costs (of which airfare is only part of the overall cost), then
book the cheaper flight (eventually). If you are constrained by time, then book the
nonstop.

Finally, while airlines do not like this, you should not overlook the possibility that a
round trip is cheaper than a one-way, given the vagaries of international fares. If
that happens, buy the round trip and throw away the return. As long as you are
not a repeat offender of this concept, there will be no problem.

I haven't flown Austrian since the last century so can't comment on them, but have traveled on Aer Lingus (note Irish spelling of Air) a couple times recently from Dulles to and from the UK. They're fine. They have a number of different fare types so you need to pick which one works best for you. We find the rock bottom one (Saver) too limiting in terms of flexibility and baggage allowance. As most airlines do, sometimes there are schedule changes between booking and flight time. This happened to me resulting in an overly long layover before my connection to Manchester but it was no problem to correct that by phone. Another time the flight from Dulles was about an hour delayed resulting in a missed connection but they were ready at the transfer desk with new boarding passes already printed for the next flight which was quite soon after. You will find complaints about any airline on travel fora like Tripadvisor. People rarely log in just to say they had a fine flight. A nonstop rather than a connection is a big advantage, but a price difference of "about half" is a big one, although again, make sure you're comparing apples to apples in terms of fare class, and the actual amount is relevant too (such as, is it the difference between $350 and $700, or between $600 and $1200?). Dublin is an efficient airport but busy. I find being able to do the US immigration/customs processing there rather than on arrival in the US to be a big advantage, but this won't matter to you if you're only flying one way to Europe.

I've flown Austrian from Vienna to Dulles twice, as recently as 2024. No complaints, but we did not have a reason to deal with customer service or flight changes. The convenience of the direct flight outweighed anything else for us, and they are United partners.

I'm confused about the OP 's post. In my experience Air Lingus, Lufthansa, Austrian,Iberian as well as United, America and Delta airlines charge the same amount for one way US to Europe trips as a round trip.
So unless you're using miles for the one way trip, it doesn't make sense financially.

Icelandair.com is the exception as far as I know, one way fares can be booked from the US to Europe, half of the round trip cost.
I have recently booked two one way fares. One to Copenhagen in July and another from Rome to Raleigh NC in October. Saga premium flex is their Business class and is refundable to original form of purchase.