Ampies are equivalent to a level 5 manyu in XP given. Matching is largely irrelevant.
As for LC, Skillblooms are hands-down the rarest option there, and if you have 6* girls, or even perhaps certain 5* girls, you might as well go for those, since LC are easily farmed in event maps ?-4 and ?-8. Manyus are nice, Ampies are nice, but both can be farmed, manyus in particular are reliably gained (and honestly, once you've played a couple months, unless you're evolving girls every few days gold isn't an issue, so you can even use level 5 manyus on level 60+ girls, so waiting for level 100s, whether from LC, SG or daily, isn't space-efficient).
Also, game WILL NOT ALLOW you to use an ampy on a girl who's maxed out on that type of ampy. Ask my Anemone