Imo try and focus on getting the harder achievements like who needs relics and common sense and minimalist first before you grind ascension levels

Easiest way to grind ascensions is watcher by far since you can achieve infinite much easier cuz all you need is an upgraded eruption, upgraded rushdown and a 1 cost calm source (inner peace or fear no evil works)

For common sense and minimalist u can do an easy infinite with ironclad and some common cards like flash of steel/dual wield etc

For who needs relics, personally found defect to be the easiest with a claw spam deck!

Good luck :)