IMO...
Will most likely come down to synergy with your system, but overall I'd say the yammy are more capable and will scale higher with quality equipment than utopia. In general, if you want something with a wetter and romantic tone I think the utopia are a better pick. If you want something that has a slightly drier yet accurate tone, I'd pick the yammy. If you want more slam, holographicness, and macrodynamics the utopia is more capable. Anything that has to do with extension, timbre, and resolution the yammy will provide. There's not much the utopia does "better" technically than the yammy, but it does have its charm at times.
On lower-end chains that I've tried, I'd likely go for the utopia. Main reason is that the bass on the yammy is too muddy on lower-end amps (I hate muddiness). There's not enough control over it, but I guess if you prioritize quantity over quality you may like the yammy more.
On my best chain, yammy all the way! It just offers more of everything, especially in the lower frequencies. The utopia used to be my pick for treble king, but the yammy easily surpasses it (ie. incredibly life-like). This was all done on an even playing field, cables included.
To summarize...
What the Utopia does better:
holographic stage
macrodynamics
smoothness
contrast
slam
What the YH5K does better:
imaging
comfort
overall timbre
microdynamics
traditional stage
energy and texture
extension both ways
overall resolution/technicalities
black background/low noise floor
stage depth, verticality, placement, boundary, openness, and airiness