I2P has been designed with "hidden services" in mind. AlphaBay, which until a few months ago was the most modern and progressive dark web market had fully moved to I2P. Stating that they saw no future in Tor, as the Tor Project refused to address major design issues even though they have heaps of money.
So far using i2p has been very nice to use and the tools are well developed. I run a node myself. The way i2p works is very interesting. Some services like Dread which provide i2p access have only been accessible via i2p in recent times due to the load on tor.
We'll have to see how i2p holds up when it inevitably takes over Tor and becomes a target of ddos itself.