Currently the only mag that will hold 30 is the Barrett and magpul. As you learned magpul is for six8 pattern only, but the Barrett can still be found from time to time. Only draw back of the Barrett is they typically have a reduced OAL.
I have used PRI gen1-gen3 in 25rd-10rd. The gen3 is OK but can sometimes have feeding issue which can be fixed with tweaking the mag lips. Max OAL typically 2.295. Gen2 are decent but then again tweaking still may be needed. Max OAL 2.295. Gen1 is gold, best mags I have ever used. Reliable and long OAL, typically over 2.295. These are hard to find but if you see it grab it especially the 15rd.
ASC is another mag maker I have used. Great product for a great price. I have used their 25rd and 15rd both new product on and old production. Every once and awhile I would get a FTF, but for a $15 mag who is complaining. If I wanted a super reliable gun I would buy a SIX8 and use magpul mags.
Have not had the chance yo use CDP, Stoner, Barrett, or D&H. So no solid opinions here on these. But I hear CDP is similar to ASC. Also hear that Barrett 30rd can have feeding issues. But these are just what I have heard and by no means solid reviews.
If I where a reloader I would get PRI gen3 till I could find a gen1, because of the uniform OAL. If I where a casual shooter ASC or CDP since they are cheap and I can buy a lot of them.