  Bitcoin and Ethereum transactions present one of the largest real-world
complex networks that are publicly available for study, including a detailed
picture of their time evolution. As such, they have received a considerable
amount of attention from the network science community, beside analysis from an
economic or cryptography perspective. Among these studies, in an analysis on
the early instance of the Bitcoin network, we have shown the clear presence of
the preferential attachment, or "rich-get-richer" phenomenon. Now, we revisit
this question, using a recent version of the Bitcoin network that has grown
almost 100-fold since our original analysis. Furthermore, we additionally carry
out a comparison with Ethereum, the second most important cryptocurrency. Our
results show that preferential attachment continues to be a key factor in the
evolution of both the Bitcoin and Ethereum transactoin networks. To facilitate
further analysis, we publish a recent version of both transaction networks, and
an efficient software implementation that is able to evaluate linking
statistics necessary for learn about preferential attachment on networks with
several hundred million edges.
