Lots of incorrect info flying around. Let's straighten some things up.
Optimum Tech is the only person I've ever seen show the U9S beat a C14S. I'm guessing he likely had the fan blowing down on the board, in which case I was able to duplicate his numbers, otherwise it's a landslide victory for the C14S if you orient the fan properly, blowing through the sink to the side panel.
AIO's stomp the C14S at the cost of pump noise.
A C14S can be used with a 120mm fan with the psu in the stock position - you just need to contact noctua for some clips.
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A C14S can be used with the included 140mm fan with the psu in the atx position for better temps.
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A C14S can be used with the included 140mm fan + 120mm slim wedged between the psu and side panel + 120mm slim on top of the C14S for even better better temps. The U9S doesn't come close.
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Trident Z RGB and Royal and Neo will fit just fine.
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The only reason to go for a U9S is guaranteed motherboard compatibility and if you want to put a 3.5" drive in for some reason. I think I heard of one gigabye board having the CPU socket too high. So punchline, don't cheap out on a board and you'll be fine.