I'm currently using qBittorrent in "mixed mode" (clearnet + i2p), and honestly it's amazing, even though there's no current DHT implementation for i2p. Sure, you have to configure your client to automatically add the i2p trackers and everything, but it's a huge step forward IMO.

I've also tested how one could "transfer" clearnet torrents to i2p and it went pretty well, even though you have to modify the original .torrent file to be accepted in some i2p trackers (I used postman tracker to test it, and they only accept torrents which all announce URLs are within i2p).

In general, I've found qBittorrent's implementation pretty stable and suitable for day-to-day use, even though it lacks some features.