electric fans

Would it be better two run 2 12 in fans or one 16 in fan and also would you prefer to handle the power by switch or a relay and temp system.....

Here's one I'm thinking about getting either with or without the relay stuff because I think it would be better to turn it on and off by a switch...

http://www.ebay.com/itm/DUAL-12-INC...pt=Motors_Car_Truck_Parts_Accessories&vxp=mtr

O and its going on my champion 26 in rad would two 12s even fit?