The NZXT Source 210 Elite already limits your option to get a good AIO solution. The case only accommodates a single rad, either a 120mm at the rear or top, or a 140mm at the top. Going with an AIO, it is recommended that at the very least you get a 240mm or 280mm radiator size for better heat dissipation/cooling using that larger surface area compared with a 120mm or 140mm. A good quality Air Cooler will beat a typical 120mm/140mm AIO setup. But an Air Cooler will have a hard time beating the cooling performance of a larger-sized rad.
So, in your situation, I would recommend getting a good-quality air cooler instead of the AIO solution (unless you change your case with a one that accommodates 240mm/280mm AIOs). If you prefer to...