Neither. Since you're a new member I'm going to assume this would be your first spider? Either of those would be awful choices for a first T. If it's not your first, pardon me for assuming. Do you have any other Ts already? We can definitely help your sort out what spider would be a good fit with our experience level.
You can easily find either of those spiders from reputable breeders or in the classifieds here but you should hold off on either until you get some experience under your belt. I don't know your history but these are not beginner friendly species.
Like everyone else said, I don’t know how many Ts you have or weather you have any experience, and I know the P. metallica is tempting, but that is an old world arboreal T that is NOT suitable for a first tarantula. I have around 20 tarantulas and I don’t even keep old world arboreals yet. If this is your first T I wouldn’t even recommend either one. Beauty is danger in the animal kingdom, but there are still some beautiful ones that are NW and good for beginners, I’d personally recommend almost the whole brachypelma genus. And keep in mind not every NW is a good choice for a first either, as every species is different and you need to do proper research before picking up ANYTHING. The P. metallica, along with most of not all Ts with “ornamental” in their common name are pretty much no go’s for a while. I am assuming this is your first T by your other threads. I’m a beginner too, so I’m not trying to be mean, just trying to give you some helpful 2 cents.
You’ll get plenty of recommendations for why you shouldn’t get either one of those as your first, so I’ll come at it with a different approach. How you respond to everyone will show if you truly were asking for advice or looking for someone else to help you rationalize a poor decision.
Although I almost choke on my words saying this, only because I’d feel bad for the T and it’s living conditions, assuming you’re in fact a new keeper:
Either one of those options will help solidify a point on why you maybe should have looked to a more beginner species. The choice is ultimately yours to make, so choose wisely. Between the two, I’d personally go for the Stirmi. Thats just my opinion though, and it doesn’t really matter because I hope to have both eventually anyways.
You will find with both you will have an intensive learning curve, and your experience in keeping T’s will show when you either kill the T or get bit. Either way, you’ll learn. It’s up to you how hard of a lesson that will be. I’m not saying it’s impossible, just saying that you may have more trouble than someone with years of experience with more advanced species.
Please keep us updated, and when you get a spider kiss please remember to write up a bite report. I’d be curious as to the effects of either.