For most builds, the Fractal Design Define R5.
They are both adaptive sync technologies that change your monitor refresh rate dynamically to reduce screen tearing. FreeSync is a more open standard initially developed by AMD and is being integrated into an increasingly large number of new monitors due to being royalty-free. G-Sync is Nvidia tech that does the same thing, but requires the monitor manufacturer to purchase an expensive proprietary module from the company.
G-Sync requires an Nvidia GPU. FreeSync does not require a specific GPU, but Nvidia refuses to integrate it into their GPUs despite it being free to use.
I’d recommend siding with FreeSync.
IPS panels: better colors and viewing angles
TN panels: faster response time, usually a bit cheaper
If you absolutely need the response time, get a TN. Otherwise get an IPS. They’re better in almost every way.
No, it’s pretty much the worst time to buy a Mac Pro as of late 2016.
Probably this one from LG.
I’d say the Dell P2715Q for best price/performance from a trusted source. There are some Korean monitors out there that are even cheaper but can occasionally be a hassle to get ahold of. Best overall no matter the cost is probably the BenQ BL3201PH.
There are great options from Asus as well, but those are the go-tos currently.
No matter what, get one that hits 60Hz.