If you were in charge of a State GOP, what sort of primary system is best?

[SteveRogers]

Open primary. Texas doesn't have party registration, which is nice because party registration is silly and it shouldn't be the state government's job to ensure party loyalty or the ideological purity of primary voters.
Proportional based on the statewide vote. If it's Texas we've got enough delegates to make it highly proportional, so let's say a 2% threshold.
Super Tuesday.

[SteveRogers]

I like CA's jungle primary myself.

Top two primaries are unfair, undemocratic, and unconstitutional because they unfairly limit voters' choices and discriminate against political minorities (Republicans in Safe D districts and vice-versa).  I'm surprised nobody has sued under the VRA to overturn it.

Explain how they limit voters' choices and discriminate against political minorities.

In safe districts and states, both general election candidates are from the same party, meaning that minority parties are disenfranchised.  If you live in Los Angeles and San Francisco and you're a Republican, you general election ballot will most likely be all Democrats; there are rural parts of California where the opposite happens and both general election candidates are Republicans.  It basically sends the message that member of minority parties don't deserve to have a candidate that represents them, simply because they're a minority.

The reason that that argument will never work in court is because there's nothing in the law that dictates that the general election candidates in safe districts must be from the same party, and you can certainly imagine scenarios where that won't be the case. On its face the law only discriminates against candidates who are less popular than other candidates, and that is certainly something that a reasonable ballot access restriction is allowed to do. I think the top-two system is less than ideal, but there simply isn't anything in the Constitution that requires states to hold conventional primaries.