About RAM: theoretically, if your mobo has only four slots and you might upgrade to 32GB in the future, then 2x8 is the way to go. However, really, 32GB will be mostly useless for quite a while still, and by the time you wanna upgrade you'll probably want to get newer RAM as a whole.
Otherwise, unless your mobo has 4-channel DRAM (and I've never seen one like that myself, however I never really looked, so IDK if that's a thing), there will be no speed difference. So whichever one is cheaper will do the job.
As for quality... I'm using Corsair Vengeance 2x8GB and I'm quite happy. Corsair in general seems to be a pretty good brand.
Otherwise, unless your mobo has 4-channel DRAM (and I've never seen one like that myself, however I never really looked, so IDK if that's a thing), there will be no speed difference. So whichever one is cheaper will do the job.
As for quality... I'm using Corsair Vengeance 2x8GB and I'm quite happy. Corsair in general seems to be a pretty good brand.