If we are just talking about size of the genome, the salamander genome is extremely repetitive and is around 15x the human genome. I seem to remember there was

If we are just talking about size of the genome, the salamander genome is extremely repetitive and is around 15x the human genome. I seem to remember there was one crustacean that was estimated to have a 100gb genome (30x human). Genome size has a lot to do with weird chromosomal segregations that happen in the history of the species. In terms of complexity, that's an interesting question. I haven't looked it up, but I am sure someone has done the study. Just something like counting unique k-mers of the genome will probably give you some kind of estimation. There are a lot of weird organisms out there with very different strategies for passing on their genome. There are organisms with program genome rearrangements (lamprey, roundworm) where somatic and germ genomes are actually different. There is an organism (I forgot the name) that literally breaks apart their genome into bunch of pieces and then put them back together differently for their somatic cells. There are also organisms with multiple nuclei (tetrahymena).