In terms of general vaulting trends for girls, it does seem like the power generated by the yurchenko is unequaled by the tsuk, on average. You really don't see girls twisting laid out tsuks much. It's pretty unusual and growing seemingly more and more so. Now this might be a question of how this skill is introduced and developed on the girls side or something, I don't know. My personal general observation is that the tsuk is useful earlier on because it's a lower "stress" entry the gymnast can learn flipping from. Some girls, if they want a 10.0 SV vault for L10/NCAA level competition, will have to move to yurchenkos. In general most coaches seem to still be introducing the tsuk, at least in the drill portion of early optional vaulting. I see little reason to never introduce it - that would be shortsighted, because it's usually much easier to get the kid flipping out of, if not doing it terribly well. Lacking reference base could lead to poor confidence in the yurchenko development. Also, "tsuk style" flipping drills tend to be easier to set up and do without spotting.
Front vaulting has been relatively highly valued, in the past for girls. But it's less common than the other two, probably largely because of the tendency towards lower back and knee injuries in female gymnasts, and the landing being harder. If any of the three aren't introduced, it's usually this one.
Yurchenkos are getting more common to introduce early. Ideally lots of drill work for pre-optional groups. I don't necessarily think it's "easier" to train in terms of the entry, but for some girls, the turnover and the landing, definitely. Some girls just are not generating the kind of power from a forward hurdle they are from a roundoff, and that makes sense to some extent. Of course L9 vault table is changing too - previously it was the same as L10, now different. So the vaulting situations at the higher levels should be a little different. Next cycle there looks to be some potential changes (proposals) to the vaulting structure across all levels.