Pat, I was hoping that Lughaidh, resident expert on Ulster Irish, would comment, but he hasn't done so yet. He has told me that Ulster Irish has the fewest diphthongs. Only three are shown in the Wikipedia article on Ulster Irish, compared with 7 plus one triphthong in Cork Irish.
That said, I think the resources available for the study of Ulster Irish are not comprehensive. As the dialect with the most speakers is Conemara, which is also central and represented in the irish-language media (TG4, etc), the simplest thing would be to learn Conemara Irish with the help of Mícheál Ó Siadhail's Learning Irish.
The diphthongs are actually not a major problem in the study of Irish at all. This is the first time I've seen someone raise this as a "difficulty".
If you listen to the pronunciation in three dialects of "ann" (meaning "there" or "in it") at
https://www.teanglann.ie/en/fuaim/ann, you can see Munster is more diphthongal. Many words are pronounced in all three dialects in that dictionary, making it easier to learn a real dialect.