Obligatory thunder rag is a joke so it doesn't really matter.
Shingen choice is optimal in the future because MP skills will become a thing (Shingen's best one is +20 burst for all), but that comes next year April. Till then Morgan might be fun to play around especially in light of the soon to come Brahma awakening. It's your choice whether minmaxing is your priority or you just wanna fuck around cause you're bored.