I'm equally and technically impressed by both Memmy and Avelon, cosmetically impressed more by Avelon (Memmy is also gorgeous), and emotionally more attached to Memmy since it was the first true native Apollo-like Lemmy adaptation and dev is super on-the-ball. Not that Avelon's is not I just can't speak to it since I haven't felt the need in my admittedly-lesser use of it compared to Memmy.
Both amazing apps and you really can't go wrong with either. I do really like Avelon's forced collapsing of all top-level comments' child comments which makes it easier to navigate the various apects people are commenting on at the top level and work your way down to more specific discssion based on your filtering of which top level comments address that which is of immediate interest to the specific readers' needs or preferred line of inquiry