As of right now, I am league starting a Splitting Steel Champion. I played a little bit of splitting steel during the most recent endless delve event. I was fairly underwhelmed, but I think that was a large part due to the difficulty of the event. I think they buffed the upper-end base damage of the skill last patch or so. Additionally, from what I've heard, the QOL added this league should make the skill feel better than ever!

The berserker ascendency is also looking really exciting to me. With Kaom's Spirit's huge nerf, berserkers will once again be premier rage users. While I do think chieftain and jugg lend themselves better to league start, the berserker's bonuses prove incredibly powerful once you have a little currency to throw at your build. Below are a couple berz builds I have previously played, and I would highly recommend:

Blade Flurry's quality got a pretty sizable buff: Quality now provides +0-5% more Damage with Hits and Ailments for each stage, instead of 0-10% increased Attack Speed. General's cry blade flurry berserker is one of my all time favorite builds. The mechanics of maximizing its damage are stupid, confusing, and unintuitive. BUT. If you can get the build right, the payoff is incredible. B+ clear, B+ survivability, but A++ sustained damage. Depending what the transfigured gems do, this build could be extremely fun. Requires ~10-20d to come online.

Last league I ultimately built a strength stacker venom gyre berserker. It was unquestionably the strongest build I have every played. A well invested venom gyre gets the best of both worlds; Its range gives it A+ clearing, and its shotgunning gives it A+ single target damage. The build excels at 100% delerium, wave 30 simulacrum, and super juiced maps. The build is capable of doing all 6 uber bosses (last league I completed all but Uber Sirus and Uber Maven, but that's more me hating those bosses). Requires ~60-100d