There was a notable difference in the Retreat Sundeck area of the ship from Apex to Beyond (bigger, more shades, two TVs at the Retreat Sundeck bar, etc). Haven't been on Ascent yet but my understanding is that every new ship in the same class will get small improvements. So if you have already experienced the Retreat on Apex, my recommendation is to try Ascent.
However, I have soft spot for Apex. I have been on three sailings on Apex since Sept 2021. I will never forget the first sailing in Greece not long after they started sailing again in 2021. 30-50% capacity and superb service/experience. I don't think we will ever get back to that level of service unless you are staying in the upper suites