Excellent
Rode many of them passes last year, absolutely fantasic, I even rode the Umbrail on a ZZR1400 (two-up) the unpaved section is smooth and well graded, but I would not want to ride it in the wet!
Agree with Stelvio not being best road to ride, we got snow at the roadside on the summit last August which made it extra special, but it is relatively congested by Alps standards (but still much less so than roads near me)
I reckon the souther ramp of La Bonnette (Restefond) is much better, it does not have clearly defined stacked hairpins, but twists and turns for about eight miles with I would guess over 100 twists / bends, most of which are second and third gear on the GS - all on wide, open, smooth, grippy tarmac, and you can see well ahead all the way down.
Of the passes you mention I remember the Oberalp (and the roads from there all the way down to Chur) being great and really liked the Fluella pass as well.
For those that have not yet been to the Alps, just do it, nothing in the UK comes close, the roads are generally in far better condition, have far more twists and turns per mile than anything in the UK and for the most part there is very little traffic, we got all the way down Bonnette without overtaking another vehicle, and often managed to ride for 10, 15, 30 minutes or even longer without seeing another vehicle and I do not recall getting held up for long once in the mountain roads (Apart from coming across a huge cycle race on the galibier)