The International G935F with Exynos is very comparable to the Snapdragon 820 one. You can check out the synthetic benchmarks in
GSMArena's review. The SD820 is a tad better with graphics benchmarks (gaming), but the difference is so minor that it doesn't matter - either will play any game you can download (if that's your thing). On a side-note, Samsung actually makes a lot of chips for Qualcomm.
The international one has all the right bands to use with AT&T and T-Mobile and their respective MVNOs and subsidiaries. It won't work with Verizon or Sprint (or their MVNOs).
Samsung does this weird thing with some of their global models where the device is only unlocked after you put the right SIM card in. I've only read about it being with the S7/S7 Edge models and ones from Europe. You have to put a European SIM card in it first, then you can use one from any other region. If it's "European SIM card only" and you try using an American one, it won't work unless you used a European one first.
http://www.androidcentral.com/your-unlocked-euro-galaxy-s7-still-region-locked-thats-not-huge-deal
So you should make sure to check with your seller (eBay, Amazon, B&H, etc) before buying.
I don't know if the international version comes with Samsung Pay. If not, you might be able to still download it. I don't know. And perhaps you won't care anyway.
I'm also not sure about KNOX security on the international one. There's 2 aspects of KNOX. One is to separate personal from business (so work/government emails don't get mixed up with personal, and the such). The other is related to the bootloader and flashing unofficial firmwares. If you're in to that kind of thing, the international one is the way to go, because the American S7s have a locked bootloader (even the T-Mobile one). If you have no idea what I'm talking about, just forget the last few sentences and move on.
If you don't mind paying the outright price of $750, getting the international G935F seems like the way to go. A co-worker of mine just got the S7 Edge, and it's a slick device. 5.5" screen, just like my OnePlus One, but it looks and feels much smaller overall due to the curved bezel-less screen. Or maybe it just seems smaller because I'm using a Nexus 6 now.
A few tips. Turn of S-Voice. It's redundant to Google Now, and it slows the phone down. It's activated by double tapping the home button, and because of that, when you tap the home button it waits to see if you're double tapping it, which gives the appearance of "lag". Turn that off. There's a bunch of stuff you can turn off or disable in the app manager, but google it first so you don't disable the wrong thing and have to do a factory reset. Also, it ships with Android Marshmallow 6.0 which has the ability to once again move apps to the SD card, but for some reason Samsung disabled that. There's a workaround thoguh(just google it)
The real advantage is that it's not from a carrier. That means you won't get all the useless carrier bloatware. It also means you'll get quicker updates, because it won't have to wait for the carriers to approve the update, add their crap, send it back to Samsung, get it back (and back and forth etc if necessary), before you get the update weeks or months later, or if at all.
The only other option would be to get a 2nd-hand one off of swappa or eBay or wherever that's been unlocked from T-Mobile or AT&T, or have a friend with one of those carriers buy one for you and then get it unlocked with a code (probably costing an additional $30-40).
A few tips:
Turn off S-Voice. It's redundant and inferior to Google Now. S-Voice is activated by double tapping the home button. So when you press the home button, it's waiting to see if you're going to press it again, giving the appearance of lag (plus it's annoying as $@#! when it keeps loading up and you don't want it to). Turn that off. It's been a while so I don't quite remember, but I think you have to load it, go into some settings from there and turn it off from there; you won't find it in the system settings, which Samsung has to make as convoluted and confusing as possible. Of course, my S4 is still on KitKat, so maybe that's changed.
Turn off/disable all the other garbage you don't need. Samsung takes the "kitchen sink" approach with TouchWiz (although it's not quite as bad now as it used to be), so there'll be a whole lot of other crap that's irrelevant to you. Don't just go randomly disabling stuff though, google it first. Otherwise you might disable the wrong thing and be forced to do a factory reset. If you're not comfortable with doing it, then don't. The phone should be fast enough even with all the extra crap.
Marshmallow brings back the ability to move apps to the SD card, but for some reason Samsung didn't use it. There's a workaround though. Apps loaded from the SD card will load slower (which I'm guessing is why Samsung disabled it?), so only bother doing it if it's an app you rarely use, or it's a big game.
Finally, the phone will have quick charge capability. Unless you need to, don't use it. The heat caused by the charge/discharge cycle is what kills batteries over time, and the S7s don't have an easily replaceable battery. Quick charge is nice when you need it, but otherwise just use an old 1A charger or the USB on your computer. You don't need to go from 27% to 100% in 45 minutes when you're home after work, taken your shoes off and watching Netflix.
I can't tell you anything about cases. I use Diztronic TPU cases on all my phones (yes, I have 4 phones, don't judge), but maybe you want more protection? I'll ask my co-worker what case he has and what he thinks of it.
