Well, it really depends on the alloys. 14K yellow can be “harder” than 18k yellow – but not always as it depends on the alloys! 18k white gold can be harder than 14k white gold, but again, not always! White golds are almost always harder than the yellow golds even at the same karatage. I know it makes little sense, but it really has to do with the alloys. Palladium-alloyed white gold is also different than nickel white gold, and every nickel white gold may be different from the other (some “need” plating to be white, others are very white on their own and do not need plating).
In my experience, yellow gold, because it is usually softer than white, may have a bit more “self-polishing” going on so that when it wears it polishes itself more. The scratches and scuffs seem to “blend” more and polish the metal more. For example, my rings were brushed 18k yellow gold when I got them. Before I soldered them, they were rubbing against each other a bit, and where they were rubbing got VERY shiny and took on a polished look, instead of scratched or scuffed. If I compare it to the white gold I had (that I cannot wear anymore) – both the nickel and palladium alloy varieties – the scratches seemed more distinguishable. However, with my palladium alloyed white gold it remained very very shiny and white as there was never any rhodium plating on it, it was white as it was, and retained a high polish as it seemed to also self-polish. The plated nickel white gold where the plating wore off got a little more dull as the plating wore since the gold underneath was not polished to the same high polish as the rhodium plating appeared.
However, I also think both yellow and white gold (yellow more so as it is usually softer) is more susceptible to thinning over time depending on the wear of it, and how it is built, whether it is cast/hand-forged, and so on. You may need to eventually get it reshanked/built up, and even sooner if it is rubbing against other rings, etc.
Platinum is actually SOFTER than the golds, so it displaces rather than flakes off. Some people really like this as the weight will always remain and for more surface damage you can polish it out. However, it does get a patina that some do not like (like me). I also do not like the colour of it as much as the golds. Also, as it is quite soft (though durable) it is more susceptible (depending again on the alloys) to denting, scratching, and so on than gold.
Personally, I am an 18k yellow gold fan because of its colour, the way it wears, its appearance, and weight. Others would say the same thing about platinum, 14k white gold, and so on. Everyone has their own preference!
ETA: If your original white gold ring cracked, it sounds like it was not cast/created properly. If white gold is not worked properly, it can be very brittle.