car rental

We've done this a number of times and have finally settled on using AutoEurope as our car rental agent.
Their rates are competitive and they spell out quite clearly what the various options are for insurance coverage and associated pricing. After some research I decided that the convoluted process required to file a claim and receive reimbursement from a credit card company in the event of a mishap was a turn-off for me, and I personally like the option thru Auto Europe of paying for the full cover and not having to worry about the details after the fact. I've never had a claim, but it's a comfort to me to know that the car return would be hassle free if I did.
The standard advice here is to ensure that you're booking a vehicle with automatic transmission - the default rental in Ireland is a standard shifter, which is probably something that you don't want to mess with if this will be your first time driving on the left.
Also, the rental car concessions at Dublin airport open very early - at 5:30 AM in some cases - making it a pretty simple matter to collect your car there upon arrival and be on your way. The concessions in the city don't open until around 9:30, after which you'd need to negotiate Dublin city traffic getting out of town - something else I wouldn't recommend if this will be your first time.
Many here advise against driving immediately after the long overnight flight from the US, but I've always found that I'm running on adrenaline after arrival and so have no qualms about doing that. It's an individual choice though and is something you need to consider as you plan your itinerary.

I drove with a standard shift car in Ireland. IF you are to driving a standard shift car (I drove one all my life at that point) it should be no problem.

You'll save a lot of money by opting for a vehicle with standard transmission, but keep in mind that you'll be doing the shifting with your left hand, on the right side of the car, while at the same time trying to master the rules of the road involved in driving on the left. That's a lot of moving parts if you're a first time driver in Ireland.
We go with standard transmissions ourselves now to save money, but didn't do so until I'd gotten comfortable with driving on the left. For our first visit many years ago I paid extra for an automatic and was very glad that I did.

Believe we went with Avis on our trip. We got an automatic and may have paid for full coverage through Avis for piece of mind, but on most trips, we get CDW through Allianz. For many credit cards, the CDW coverage is secondary insurance. Read your card’s benefits carefully.

We used AutoEurope as well for our trip in Ireland last year. I booked early and ended up cancelling and rebooking twice because the rates got better. Easy Peasy

Robert's advice is spot on.
We used AutoEurope last year, and the rental was with Alamo/Dublin airport. Our experience was excellent all the way around. My American Express card will cover Ireland but I opted to pay for CDW for the same reasons Robert mentioned. I would definitely get the automatic transmission if this is your first time driving on the left. There's enough to think about with narrow roads, roundabouts, and nonexistent shoulders on the rural roads. Also get the smallest car you can comfortably fit in--you'll be glad you did.

Get a letter from your credit card company stating they will cover you in Ireland. When I rented a car at Dublin Airport in 2018 they told me if I had a letter they would accept it. Good luck!

I had a car versus protruding gate latch problem in 2016 (while leaving the rental lot!), and despite the outrageous repair estimate of $4000, my credit card company refunded my bail in just a week or so. I did have to front the money via credit card at check in, but it never actually changed hands. The credit card folks actually overpaid my rental bill, eliminating the extra driver coverage. The worst part of the experience was that I had to drive around for two weeks with the damaged car since I wasn't willing to delay the start any more than the rental process had already caused. There's always the hard sell on the CDW - I think that's their profit margin.

I largely agree with you Robert. I use Auto Europe and have had absolutely no difficulty. Driving on the left is more difficult than folks expect. My disagreement is using a credit card for insurance. I have used it twice (different cards), once after something in the road cut my tire on your home island of Kauai, and the second in Iceland when a rock cracked the windshield. Each time credit card insurance covered the charge in full.

I'd advise an abundance of caution when trying to sort out the matter of rental car insurance in Ireland. Most US credit cards specifically exclude coverage there ... and in Northern Ireland as well. Some of the Elite cards do provide coverage, but you really need to drill down into their terms and conditions to understand exactly what's covered, what isn't, the procedure for filing a claim, etc. You'll then need to contact the rental car company to verify what their policy is regarding proof of insurance in order to avoid an unpleasant surprise at the check-in desk upon arrival.
It doesn't help that most of the rental car company websites make it difficult to arrive at an apples-to-apples comparison of rates and insurance coverages. One of the few that spells things out clearly up front is the aforementioned Dan Dooley, which many here swear by.
Point being that there's a lot of due diligence required to ensure that you're covered (and for what). The TripAdvisor forum is indeed a good resource, but take care that the information you read is current - things seem to change every few months or so. A simple Google search can be educational as well.
After going thru this myself on one of our first visits to Ireland I finally decided to just go with AutoEurope for the peace of mind involved.

Edited to add: you'll want to ensure that this is resolved before you depart on your trip. There's nothing worse than showing up at the rental car counter at Dublin Airport assuming that you have coverage, realizing that you don't thanks to the CC exclusion for Ireland, then having to pay thru the nose on the spot for the company's insurance before you can take custody of the vehicle . Ask me how I know this ...