I think Truss would probably be the best outcome in terms of long term prospects of keeping the loonies out of power. Realistically almost the whole Tory party are extremists at this point in one way or another so bring them out into the open under a complete plonker and let them keep shooting themselves in the foot.
The problem with Sunak would be that despite being quite a fool on the economic front, his only real selling point, he has enough of a track record in finance and as chancellor to hoodwink everybody for quite a long time I fear.
The only one who actually seems vaguely principled and genuinely horrified at the open sewer of Boris' government is Tugendhat, but I'm pretty sure a lot of his principles are primarily based on easily disprovable, damaging beliefs about the economy and society that we really need to move away from (benefit fieves, trickle down economics, light touch regulation except for when I want to control you etc). As such I'll be very happy for him not to get the top job and fool the "magic money tree" munchers once again.