with exception of Byteball they don't have any transaction fees.
they all can handle more or less the same number of TPS or so they claim. Byteball: 100, IOTA: 500, NANO: 1000
the confirmation times are instant.
as far as i can tell there is a certain centralization about them, for instance you can not run a byteball witness node! the dev decides who runs that. not sure about others.
this is just things that i can remember from these coins. i would love to see some decent in depth and unbiased comparison if someone has it.
Well, IOTA seems to be the most popular DAG cryptocurrency, IMO. It has seen a surge in price last year, and interest among investors since its focus is on the Internet of Things. On the other hand, Nano's focus is on fast and cheap micropayments for the world but not as popular as IOTA. If we were to compare the various DAG cryptocurrencies available, they're all the same in terms of scalability, as their speeds are relatively instant, and their scalability is infinite.
By the way, there's a new kid on the block which is called Hedera Hashgraph. It claims to be far more superior than Bitcoin and Ethereum in terms of TPS and low costs, but if you investigate its technicalities, you'll notice that it's just another DAG cryptocurrency. It shares many things in common of various DAG cryptocurrencies such as Byteball, IOTA, and NANO. As such, I believe that Hashgraph is nothing more than pure hype.
Nonetheless, as well as you do, I would love to see some deep comparisons between different DAG cryptocurrencies. Many of them claim high TPS and low costs, but they would need to be put up to the test in order to determine how their throughput would be with high network load. Perhaps, DAG is the future of cryptocurrency and Blockchain's successor, or perhaps not. All we must do is wait and see if cryptocurrencies that make use of a DAG gain mainstream adoption in the long run. Just my thoughts