Andalusia in early April--or southern Italy?

I've stayed in Andalucia several times in April, sometimes there may be a day or two of rain whilst other times it will be sunny and warm. I've been in Rome and Sorrento in February and April and those occasions have been sunny and warm.

It's always a tough one to call but it is highly unlikely to be any way like your Irish experience. Ireland is at the forefront of many Atlantic weather fronts that frequently bring rain, it's why it's so lush and green. Andalucia and Italy don't experience these fronts so good weather can be almost guaranteed. There are very few places where the threat of rain can be almost exclusively ruled out but as Andalucia has an average of 320 sunny days per year I think you can afford a bit of optimism.

You have to get over one past raining while traveling experience or don't go;
the weather is luck of the draw.

I was in Andalusia in April 4-15 this year, and there wasn’t a single day of rain. Weather was perfect for sightseeing- cool in the morning, warming up in the afternoon and staying warm till late evening.
On the other hand in Italy the same time of the year, I encountered several rainy days- in Positano, Sorrento and in Rome.
I always travel in April- May or in the fall, and never leave without an umbrella and rain jacket.

Weather in Europe is unpredictable. In general, early April is a great time for both. Andalucia is the warmest, driest part of Europe but it does rain. My guess is that if there's bad weather coming through, it will hit both places. Ireland is (in)famous for its rain - that's why it's soooo green.

If weather is your only criterion, flip a coin. Seriously, it probably doesn't matter.

Go to Spain. I spent the entire month of April there in 2012 and it was great. The weather was unseasonably cold but still dry. People kept appologizing about the weather because we needed jackets. I was able to experience Semana Santa (especially in Zaragosa) and April Fair in Sevilla, both were very memorable. Customer service is night and day between Spain and Italy (especially southern Italy) and Spain is one of the least expensive places in Europe (outside of Barcelona and Madrid).

I was in Andalucia in late March 2017, and aside from one VERY cold morning in Granada at the Alhambra (about 32 degrees!) the weather was mild and dry. It was ideal sightseeing weather!