K1 is a fiancé visa. You still have to get married, pay to adjust status, pay for work authorization, pay for travel authorization and wait for a long time to get a greencard in hand. You can't work or travel outside of the US and are completely dependent on your partner until work authorization is issued. On top of that, you'll have to wait to remove conditions.
CR1 or spousal visa will allow you to apply, go through consular processing while in Ireland, still working, still making money, and with time to make proper plans on how you intend to enter the US. When the time comes and you do enter the US, you will already have work authorization and be able to travel cross border freely. If you haven't yet been married for 2 years when you do cross with your visa, you will still have to remove conditions. You could do a quick courthouse wedding to get the ball rolling and plan a ceremony and reception at a later date.
You guys have to factor in things like has your fiancé filed US income tax for the last 3 years? Who will be your financial sponsor? How are you going to take care of business back in Ireland if you can't travel? What property do you need to dispose of back in Ireland? What job does your fiancé have in the US to support the 2 of you? Where are you going to live? Do you have enough savings to pay first and last months rent and utility hook ups in the US? How are you going to afford health insurance in the US? How are you going to afford a vehicle and insurance in the US? Does she have a bank account and a positive US credit history? Et cetera...
From what it sounds like, in your current situation, you are together, you're working, you're living life in Ireland. With a CR1, you can remain together, save money, plan a proper move and be prepared. Most people who come from western countries who are used to independence have a really hard time becoming 100% dependent on their partner. This can become taxing on the relationship and possibly lead to it breaking down. Immigration is not cheap, fast or for the faint of heart, so you really should take the time to consider everything before diving in head first.