Greetings
Although I am a big Semogue fan I have nothing whatsoever against Omega boars, they are however completely different. Semogue boars take a long while to break in and tend to bloom a lot and the knot looks rather scruffy, this does not affect in any way the performance.
Omega's on the other hand have more compact knots made of bristle that seems to be more tapered throughout it's length and thicker at the base, the tips are about the same as the Semogue's, this tends to result in a more compact knot that does not bloom as much, they stay neat looking even after prolonged use.
It's very much personal choice I only have a couple of Omega's but have several Semogues and feel entitled to give a personal opinion on them. The SOC is a great brush but a lather eater, the 830 is rather soft and better for creams and bowl lathering , the 620 has been made for face lathering and does that job superbly, the 2000 is a whopper of a brush and really only suitable for bowl lathering.
I personally rate the 1800 as the best of the bunch great for face lathering it could be used for bowl lathering, it does have a wooden handle which not everybody likes; I do.
Going by your criteria the best choice might well be the Semogue 610 (in the Semogue range) it has a plain non dyed knot and an acrylic handle, I do not own this brush but understand it performs similar to the 620.
Regards
Dick