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I have 9...
3 skorchas,
3 rokits
3 grotzookas

generally i run them as homogenous squadrons. What about one of each in each squadron?

I vote for homogenous squadrons since those different weapons should target different unit types and a squadron has to fire together at the same unit. You will reduce the effectiveness of some weapons if you mix them within a unit.

Do you want to shoot rokkits at infantry? Do you want to shoot shoot flamers at vehicles?

There's your answer right there

Flamers are a really bad loadout for kanz anyways.

grotzookas are the kan weapon of choice for infantry for sure. skorchas just miss the benefit of their BS. better choice on a dread if anything.

rokkits are very cost effective indeed, but i am also partial to KMBs - great anti terminators without having to worry about getting hot. a very nasty suprose for marine players who werent expecting any AP2 in an ork army. let alone accurate AP2!
if points are spare then its just a better version of a rokkit in the hands of a kan. less cost efficient on average sure, but a better gun nonetheless.
pointless against foes where AP2 is useless of course. get the cheaper rokkits.

id defo keep squds similarly armed as above, but id doll those skorchas up into KMBs if playing WYSIWYG, and if not, id use them as grotzookas or rokkits depending on your foe and army list

Definitely go homogenous, i.e. each whole squad armed identically. Then you can pick an appropriate target for the squad and dish out some serious hurt, which you are unlikely to be able to do with a mixed squad.