Currently, I would say orisa is only good with sigma and is at best acceptable with any other tank. The reason?

Orisa desperately needs a shield in front of her in order to be viable, and her own shield isn't enough. In order to apply pressure with her gun, orisa must both:

1) move slowly (while having a fat hit box)

2) Be in LOS of the target she fires at the entire time.

In comparison, sigma gets to move at full speed and spend a significant amount of time while poking around a corner. As a result, orisa must take far more damage then either sigma, hog, zarya, etc. would take in order to poke. However, this weakness can be negated when orisa has a shield in front of her.

Before sigma came out, orisa was quite good but in an ok spot since her shield was much stronger then, to the point of rivaling rein's shield. However, since blizzard thought the best way to nerf double shield way back when was to simply nerf the shields themselves, all they have done is put themselves in a pickle where orisa is nearly completely dependent on sigma's shield to circumvent the downsides her gun has.

I think transferring power in orisa's kit to her shield and doing the opposite for sigma would do a lot of good for the game in a variety of ways:

1) They both could get nerfed to the appropriate strength without worry that doing so would render the other OP/UP

2) ​Less double shield of course

3) When sigma is picked as an off tank with rein or winston, it would be more bearable since he wouldn't be adding much more shielding to the mix.

3) orisa could be played with hog again, and combos like orisa/zarya and orisa/ball might not be throw picks.

4) in low ranks, orisa would become more of an alternative to rein; low ranks have always greatly favored rein because a shield helps cover up bad positioning.

I think I would like to see a patch along the lines of:

Orisa:

• Shield: 600 hp -> 800hp,
• fortify: no longer prevents headshots and 40% dmg resist -> 20% dmg resist

Sigma:

• Shield: 700hp -> 500hp and 80hp/s regen -> 60 hp/s regen
• Kinetic grasp: cooldown 12sec -> 10sec, shield conversion rate from 60%->80%

These changes aren't be to buff or nerf either of them to the appropriate level, but simply to decouple orisa from sigma while keeping them roughly at the strength they are at now.

tl;dr sigma shield hard enables orisa