2k, 2k 144hz, 2k curved, 2k curved 144hz or 4k.

the title says it all... I have money to spend tho if its not mandatory I would like to no spend it... I have 2 monitors of full hd (1080p) and I just bought a beast pc (gtx 1080, i7 8870k 8th gen, 16 gb 2400 ram, a new motherboard and such) and I figured those are the important parts of my pc and it is barely bottlenecked by internal stuff, and I came to realization that the part that is making my games look lame, is my monitor... so as the title says, what should I buy?
 

the last game I played competitively was overwatch, csgo was before, the main game I play now is ark:survival evolved but that will probably pass in a abit… im thinking of buying rainbow six siege and im waiting for the next overwatch/csgo like game to come out so I can play hours upon hours on it
but the main game im looking for is rainbow