I think it is quite straightforward.
Standard steel studs have a very precise thread fit and work well in any Aluminium engine case.
We use standard steel studs on all of our 2.0, 3.0 and 3.2 Aluminium engines. (We don't deal with 3.6 litre engines routinely so I would extend my comments to these engines). We do use them with a 12 point flange nut and ground martensitic stainless steel washers.
I find it hard to justify the cost of Aftermarket studs as I don't really see the engineering benefits.
I believe that old, thermally stressed Magnesium Cases need all the help they can get to survive.
The reduced expansion forces - (about 250lbs of increase compared to 1500lbs for a steel stud) must be good idea.
I worry about Dilavar but as few cars now see salty roads it is less of a concern and the coating will go a long way to eliminating the issues we have seen and this would be my general recommendation.
I also worry about Aftermarket Steel Studs with an increased shank diameter on Magnesium Cases the pull out forces will increase in proportion to the square of the shank diameter. If the shank is 9.5mm diameter the pull out force will increase from 1500lbs to around 2300lbs.
We use 6AL4V-ELI Titanium Studs for Magnesium Engines. The COE is not quite as good but the reduced Young's Modulus helps.
These studs keep the expansion forces to around 500 lbs and we will never have any corrosion issues.
The latest version has a 'dog point' on the case end. This allows them to be lightly torque tightened before the thread locker sets and ensures that case threads are loaded evenly. (We haven't taken photographs yet)
We are also planning a steel version to suit 3.6 litre engines and they will also have a dog point.