OK, so I have read through the thread where the Red Flag Flying self-proc was discovered and discussed, and it is my go-to monk loadout now. In that thread y'all pointed out that it is much less risky in the offhand, but will still crash the game if player accuracy exceeds enemy defense by over 100 points (every hit is a crit). After playing for over 100 hours with Mohora Tanga in my monk's offhand I think there may be more to it.
Even with multiple stacks of +20 accuracy from Scordio's Edge + SoF (like 5+ when I've tested it), I never crash the game when it is in my offhand unless I do a regular auto-attack. If I use any other active ability that does a full attack (such as stunning blow) it has never crashed the game, even though I get massive Red Flag Flying chains. One thing I have noticed is that the animation from the standard auto-attack will often attack with the offhand weapon first (and these are the only times I crash my game), but a full attack ability will always attack with the primary weapon first, then the offhand.
I have not tested this with Entropy or other 100% crit conversion methods yet, but my accuracy has been so high that it is in effect the same thing.
@Boeroer did you ever crash the game with an active ability full attack, or was it always with auto attacks? I am curious if I am on to something here, or if it is just the luck of many, many draws.
Also worth noting that I strictly play turn-based. Not sure if that matters.
To the OP: my vote is 1) Magran's Favor (main) + Mohora Tanga (offhand) for single target annihilation or 2) one of the mortars (main) + Mohora Tanga (offhand) for widespread destruction. You can add bolt catchers, etc., but it is not needed if you have some way of boosting your accuracy. I see Mohora Tanga as a worker thread that proceeds in the background allowing you to attack over and over with the main hand weapon due to Swift Flurry/HBD procs, so there is much less need for a multi-hit weapon in the main hand. Then the question becomes: which one-handed weapon is best to hit with over and over? In my estimation, this seems to be something with Bleeding Cut for single targets and multi-hit mortar AOEs for groups.
Seeker's Fang is, of course, also great if you want to MC with Cipher, particularly if you are willing to make a bunch of Soul Blade max focus stacks permanent with SoF/CG - then you are holding an absolute nuke that deals massive raw damage and basically has its own version of Bleeding Cut. Also has a cool multi-hit cone AOE once/encounter that won't proc Swift Flurry/HBD, but will proc the giant raw DOT once on each target and the smaller, but stackable raw DOT three times on each target. With the potentially sky-high intelligence of the monk, the cone is actually pretty good sized too.