Easton Haven for sure 🙂
I have owned 6 different Thomson stems (2 x Elite and 4 x X4)
more recently I have owned the Haven stem and the Renthal Duo stem, I still use the haven with Renthal 750mm bars on my mountain bike
the Haven is noticeably more ‘solid’ than the X4 when really cranking on the bars, especially with wider bars (i.e. 750mm+) yet comes in lighter too
before moving to wider bars, I never had any issue with the Thomson stem feeling flexible
when you look at the Haven, its a blatant rip-off of the Thomson X4 stem, but with a wider bar clamp, wider body and Easton’s Top-Lock clamp technology